From: Björn Töpel <bjorn@rivosinc.com>

Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
dynamic resizing of virtual machine memory, and requires proper
hotplugging (add/remove) support to work.

Add device memory support for RISC-V "virt" machine, and enable
virtio-md-pci with the corresponding missing hotplugging callbacks.

Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
---
 hw/riscv/Kconfig       |  2 +
 hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
 hw/virtio/virtio-mem.c |  5 ++-
 3 files changed, 87 insertions(+), 3 deletions(-)

diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
index a2030e3a6ff0..08f82dbb681a 100644
--- a/hw/riscv/Kconfig
+++ b/hw/riscv/Kconfig
@@ -56,6 +56,8 @@ config RISCV_VIRT
     select PLATFORM_BUS
     select ACPI
     select ACPI_PCI
+    select VIRTIO_MEM_SUPPORTED
+    select VIRTIO_PMEM_SUPPORTED
 
 config SHAKTI_C
     bool
diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index 4fdb66052587..443902f919d2 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -53,6 +53,8 @@
 #include "hw/pci-host/gpex.h"
 #include "hw/display/ramfb.h"
 #include "hw/acpi/aml-build.h"
+#include "hw/mem/memory-device.h"
+#include "hw/virtio/virtio-mem-pci.h"
 #include "qapi/qapi-visit-common.h"
 #include "hw/virtio/virtio-iommu.h"
 
@@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
     DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
     int i, base_hartid, hart_count;
     int socket_count = riscv_socket_count(machine);
+    hwaddr device_memory_base, device_memory_size;
 
     /* Check socket count limit */
     if (VIRT_SOCKETS_MAX < socket_count) {
@@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
         exit(1);
     }
 
+    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
+        error_report("unsupported amount of memory slots: %"PRIu64,
+                     machine->ram_slots);
+        exit(EXIT_FAILURE);
+    }
+
     /* Initialize sockets */
     mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
     for (i = 0; i < socket_count; i++) {
@@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
     memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
                                 mask_rom);
 
+    /* device memory */
+    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
+                                  GiB);
+    device_memory_size = machine->maxram_size - machine->ram_size;
+    if (device_memory_size > 0) {
+        /*
+         * Each DIMM is aligned based on the backend's alignment value.
+         * Assume max 1G hugepage alignment per slot.
+         */
+        device_memory_size += machine->ram_slots * GiB;
+
+        if (riscv_is_32bit(&s->soc[0])) {
+            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
+                                                          GiB);
+
+            if (memtop > UINT32_MAX) {
+                error_report("memory exceeds 32-bit limit by %lu bytes",
+                             memtop - UINT32_MAX);
+                exit(EXIT_FAILURE);
+            }
+        }
+
+        if (device_memory_base + device_memory_size < device_memory_size) {
+            error_report("unsupported amount of device memory");
+            exit(EXIT_FAILURE);
+        }
+
+        machine_memory_devices_init(machine, device_memory_base,
+                                    device_memory_size);
+    }
+
     /*
      * Init fw_cfg. Must be done before riscv_load_fdt, otherwise the
      * device tree cannot be altered and we get FDT_ERR_NOSPACE.
@@ -1712,12 +1752,21 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
     MachineClass *mc = MACHINE_GET_CLASS(machine);
 
     if (device_is_dynamic_sysbus(mc, dev) ||
-        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
+        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI) ||
+        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
         return HOTPLUG_HANDLER(machine);
     }
     return NULL;
 }
 
+static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
+                                            DeviceState *dev, Error **errp)
+{
+    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_pre_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
+    }
+}
+
 static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
                                         DeviceState *dev, Error **errp)
 {
@@ -1735,6 +1784,35 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
     if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
         create_fdt_virtio_iommu(s, pci_get_bdf(PCI_DEVICE(dev)));
     }
+
+    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
+    }
+}
+
+static void virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
+                                                  DeviceState *dev,
+                                                  Error **errp)
+{
+    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_unplug_request(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev),
+                                     errp);
+    } else {
+        error_setg(errp,
+                   "device unplug request for unsupported device type: %s",
+                   object_get_typename(OBJECT(dev)));
+    }
+}
+
+static void virt_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
+                                          DeviceState *dev, Error **errp)
+{
+    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
+        virtio_md_pci_unplug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
+    } else {
+        error_setg(errp, "virt: device unplug for unsupported device"
+                   " type: %s", object_get_typename(OBJECT(dev)));
+    }
 }
 
 static void virt_machine_class_init(ObjectClass *oc, void *data)
@@ -1757,7 +1835,10 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
     assert(!mc->get_hotplug_handler);
     mc->get_hotplug_handler = virt_machine_get_hotplug_handler;
 
+    hc->pre_plug = virt_machine_device_pre_plug_cb;
     hc->plug = virt_machine_device_plug_cb;
+    hc->unplug_request = virt_machine_device_unplug_request_cb;
+    hc->unplug = virt_machine_device_unplug_cb;
 
     machine_class_allow_dynamic_sysbus_dev(mc, TYPE_RAMFB_DEVICE);
 #ifdef CONFIG_TPM
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index ffd119ebacb7..6636e5e1089c 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -51,7 +51,8 @@ static uint32_t virtio_mem_default_thp_size(void)
 {
     uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
 
-#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
+#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__) \
+    || defined(__riscv__)
     default_thp_size = 2 * MiB;
 #elif defined(__aarch64__)
     if (qemu_real_host_page_size() == 4 * KiB) {
@@ -161,7 +162,7 @@ static bool virtio_mem_has_shared_zeropage(RAMBlock *rb)
  * necessary (as the section size can change). But it's more likely that the
  * section size will rather get smaller and not bigger over time.
  */
-#if defined(TARGET_X86_64) || defined(TARGET_I386)
+#if defined(TARGET_X86_64) || defined(TARGET_I386)  || defined(TARGET_RISCV)
 #define VIRTIO_MEM_USABLE_EXTENT (2 * (128 * MiB))
 #elif defined(TARGET_ARM)
 #define VIRTIO_MEM_USABLE_EXTENT (2 * (512 * MiB))
-- 
2.40.1

On 5/21/24 07:56, Björn Töpel wrote:
> From: Björn Töpel <bjorn@rivosinc.com>
> 
> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
> dynamic resizing of virtual machine memory, and requires proper
> hotplugging (add/remove) support to work.
> 
> Add device memory support for RISC-V "virt" machine, and enable
> virtio-md-pci with the corresponding missing hotplugging callbacks.
> 
> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
> ---
>   hw/riscv/Kconfig       |  2 +
>   hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>   hw/virtio/virtio-mem.c |  5 ++-
>   3 files changed, 87 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
> index a2030e3a6ff0..08f82dbb681a 100644
> --- a/hw/riscv/Kconfig
> +++ b/hw/riscv/Kconfig
> @@ -56,6 +56,8 @@ config RISCV_VIRT
>       select PLATFORM_BUS
>       select ACPI
>       select ACPI_PCI
> +    select VIRTIO_MEM_SUPPORTED
> +    select VIRTIO_PMEM_SUPPORTED
>   
>   config SHAKTI_C
>       bool
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index 4fdb66052587..443902f919d2 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -53,6 +53,8 @@
>   #include "hw/pci-host/gpex.h"
>   #include "hw/display/ramfb.h"
>   #include "hw/acpi/aml-build.h"
> +#include "hw/mem/memory-device.h"
> +#include "hw/virtio/virtio-mem-pci.h"
>   #include "qapi/qapi-visit-common.h"
>   #include "hw/virtio/virtio-iommu.h"
>   
> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>       DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>       int i, base_hartid, hart_count;
>       int socket_count = riscv_socket_count(machine);
> +    hwaddr device_memory_base, device_memory_size;
>   
>       /* Check socket count limit */
>       if (VIRT_SOCKETS_MAX < socket_count) {
> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>           exit(1);
>       }
>   
> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
> +        error_report("unsupported amount of memory slots: %"PRIu64,
> +                     machine->ram_slots);
> +        exit(EXIT_FAILURE);
> +    }
> +
>       /* Initialize sockets */
>       mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
>       for (i = 0; i < socket_count; i++) {
> @@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
>       memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
>                                   mask_rom);
>   
> +    /* device memory */
> +    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
> +                                  GiB);
> +    device_memory_size = machine->maxram_size - machine->ram_size;
> +    if (device_memory_size > 0) {
> +        /*
> +         * Each DIMM is aligned based on the backend's alignment value.
> +         * Assume max 1G hugepage alignment per slot.
> +         */
> +        device_memory_size += machine->ram_slots * GiB;

We don't need to align to 1GiB. This calc can use 2MiB instead (or 4MiB if we're
running 32 bits).

> +
> +        if (riscv_is_32bit(&s->soc[0])) {
> +            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
> +                                                          GiB);

Same here - alignment is 2/4 MiB.

> +
> +            if (memtop > UINT32_MAX) {
> +                error_report("memory exceeds 32-bit limit by %lu bytes",
> +                             memtop - UINT32_MAX);
> +                exit(EXIT_FAILURE);
> +            }
> +        }
> +
> +        if (device_memory_base + device_memory_size < device_memory_size) {
> +            error_report("unsupported amount of device memory");
> +            exit(EXIT_FAILURE);
> +        }

Took another look and found this a bit strange. These are all unsigned vars, so
if (unsigned a + unsigned b < unsigned b) will always be 'false'. The compiler is
probably cropping this out.

The calc we need to do is to ensure that the extra ram_slots * alignment will fit into
the VIRT_DRAM block, i.e. maxram_size + (ram_slots * alignment) < memmap[VIRT_DRAM].size.


TBH I'm starting to have second thoughts about letting users hotplug whatever they want.
It seems cleaner to just force the 2/4 Mb alignment in pre_plug() and be done with it,
no need to allocate ram_slots * alignment and doing all these extra checks.

As I sent in an earlier email, users must already comply to the alignment of the host
memory when plugging pc-dimms, so I'm not sure our value/proposition with all this
extra code is worth it - the alignment will most likely be forced by the host memory
backend, so might as well force ourselves in pre_plug().


Thanks,


Daniel


> +
> +        machine_memory_devices_init(machine, device_memory_base,
> +                                    device_memory_size);
> +    }
> +
>       /*
>        * Init fw_cfg. Must be done before riscv_load_fdt, otherwise the
>        * device tree cannot be altered and we get FDT_ERR_NOSPACE.
> @@ -1712,12 +1752,21 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
>       MachineClass *mc = MACHINE_GET_CLASS(machine);
>   
>       if (device_is_dynamic_sysbus(mc, dev) ||
> -        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
> +        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI) ||
> +        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
>           return HOTPLUG_HANDLER(machine);
>       }
>       return NULL;
>   }
>   
> +static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
> +                                            DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_pre_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
> +    }
> +}
> +
>   static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>                                           DeviceState *dev, Error **errp)
>   {
> @@ -1735,6 +1784,35 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>       if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
>           create_fdt_virtio_iommu(s, pci_get_bdf(PCI_DEVICE(dev)));
>       }
> +
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
> +    }
> +}
> +
> +static void virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
> +                                                  DeviceState *dev,
> +                                                  Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_unplug_request(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev),
> +                                     errp);
> +    } else {
> +        error_setg(errp,
> +                   "device unplug request for unsupported device type: %s",
> +                   object_get_typename(OBJECT(dev)));
> +    }
> +}
> +
> +static void virt_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
> +                                          DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_unplug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
> +    } else {
> +        error_setg(errp, "virt: device unplug for unsupported device"
> +                   " type: %s", object_get_typename(OBJECT(dev)));
> +    }
>   }
>   
>   static void virt_machine_class_init(ObjectClass *oc, void *data)
> @@ -1757,7 +1835,10 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
>       assert(!mc->get_hotplug_handler);
>       mc->get_hotplug_handler = virt_machine_get_hotplug_handler;
>   
> +    hc->pre_plug = virt_machine_device_pre_plug_cb;
>       hc->plug = virt_machine_device_plug_cb;
> +    hc->unplug_request = virt_machine_device_unplug_request_cb;
> +    hc->unplug = virt_machine_device_unplug_cb;
>   
>       machine_class_allow_dynamic_sysbus_dev(mc, TYPE_RAMFB_DEVICE);
>   #ifdef CONFIG_TPM
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index ffd119ebacb7..6636e5e1089c 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -51,7 +51,8 @@ static uint32_t virtio_mem_default_thp_size(void)
>   {
>       uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
>   
> -#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
> +#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__) \
> +    || defined(__riscv__)
>       default_thp_size = 2 * MiB;
>   #elif defined(__aarch64__)
>       if (qemu_real_host_page_size() == 4 * KiB) {
> @@ -161,7 +162,7 @@ static bool virtio_mem_has_shared_zeropage(RAMBlock *rb)
>    * necessary (as the section size can change). But it's more likely that the
>    * section size will rather get smaller and not bigger over time.
>    */
> -#if defined(TARGET_X86_64) || defined(TARGET_I386)
> +#if defined(TARGET_X86_64) || defined(TARGET_I386)  || defined(TARGET_RISCV)
>   #define VIRTIO_MEM_USABLE_EXTENT (2 * (128 * MiB))
>   #elif defined(TARGET_ARM)
>   #define VIRTIO_MEM_USABLE_EXTENT (2 * (512 * MiB))

On 24.05.24 15:14, Daniel Henrique Barboza wrote:
> 
> 
> On 5/21/24 07:56, Björn Töpel wrote:
>> From: Björn Töpel <bjorn@rivosinc.com>
>>
>> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
>> dynamic resizing of virtual machine memory, and requires proper
>> hotplugging (add/remove) support to work.
>>
>> Add device memory support for RISC-V "virt" machine, and enable
>> virtio-md-pci with the corresponding missing hotplugging callbacks.
>>
>> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
>> ---
>>    hw/riscv/Kconfig       |  2 +
>>    hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>>    hw/virtio/virtio-mem.c |  5 ++-
>>    3 files changed, 87 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
>> index a2030e3a6ff0..08f82dbb681a 100644
>> --- a/hw/riscv/Kconfig
>> +++ b/hw/riscv/Kconfig
>> @@ -56,6 +56,8 @@ config RISCV_VIRT
>>        select PLATFORM_BUS
>>        select ACPI
>>        select ACPI_PCI
>> +    select VIRTIO_MEM_SUPPORTED
>> +    select VIRTIO_PMEM_SUPPORTED
>>    
>>    config SHAKTI_C
>>        bool
>> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>> index 4fdb66052587..443902f919d2 100644
>> --- a/hw/riscv/virt.c
>> +++ b/hw/riscv/virt.c
>> @@ -53,6 +53,8 @@
>>    #include "hw/pci-host/gpex.h"
>>    #include "hw/display/ramfb.h"
>>    #include "hw/acpi/aml-build.h"
>> +#include "hw/mem/memory-device.h"
>> +#include "hw/virtio/virtio-mem-pci.h"
>>    #include "qapi/qapi-visit-common.h"
>>    #include "hw/virtio/virtio-iommu.h"
>>    
>> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>>        DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>>        int i, base_hartid, hart_count;
>>        int socket_count = riscv_socket_count(machine);
>> +    hwaddr device_memory_base, device_memory_size;
>>    
>>        /* Check socket count limit */
>>        if (VIRT_SOCKETS_MAX < socket_count) {
>> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>>            exit(1);
>>        }
>>    
>> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
>> +        error_report("unsupported amount of memory slots: %"PRIu64,
>> +                     machine->ram_slots);
>> +        exit(EXIT_FAILURE);
>> +    }
>> +
>>        /* Initialize sockets */
>>        mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
>>        for (i = 0; i < socket_count; i++) {
>> @@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
>>        memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
>>                                    mask_rom);
>>    
>> +    /* device memory */
>> +    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
>> +                                  GiB);
>> +    device_memory_size = machine->maxram_size - machine->ram_size;
>> +    if (device_memory_size > 0) {
>> +        /*
>> +         * Each DIMM is aligned based on the backend's alignment value.
>> +         * Assume max 1G hugepage alignment per slot.
>> +         */
>> +        device_memory_size += machine->ram_slots * GiB;
> 
> We don't need to align to 1GiB. This calc can use 2MiB instead (or 4MiB if we're
> running 32 bits).
> 
>> +
>> +        if (riscv_is_32bit(&s->soc[0])) {
>> +            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
>> +                                                          GiB);
> 
> Same here - alignment is 2/4 MiB.
> 
>> +
>> +            if (memtop > UINT32_MAX) {
>> +                error_report("memory exceeds 32-bit limit by %lu bytes",
>> +                             memtop - UINT32_MAX);
>> +                exit(EXIT_FAILURE);
>> +            }
>> +        }
>> +
>> +        if (device_memory_base + device_memory_size < device_memory_size) {
>> +            error_report("unsupported amount of device memory");
>> +            exit(EXIT_FAILURE);
>> +        }
> 
> Took another look and found this a bit strange. These are all unsigned vars, so
> if (unsigned a + unsigned b < unsigned b) will always be 'false'. The compiler is
> probably cropping this out.

No. Unsigned interger overflow is defined behavior and this is a common 
check to detect such overflow. tI's consistent with what we do for other 
architectures.

> 
> The calc we need to do is to ensure that the extra ram_slots * alignment will fit into
> the VIRT_DRAM block, i.e. maxram_size + (ram_slots * alignment) < memmap[VIRT_DRAM].size.
> 
> 
> TBH I'm starting to have second thoughts about letting users hotplug whatever they want.
> It seems cleaner to just force the 2/4 Mb alignment in pre_plug() and be done with it,
> no need to allocate ram_slots * alignment and doing all these extra checks.

It's worth noting that if user space decides to specify addresses 
manually, it can mess up everything already. There are other events that 
can result in fragmentation of the memory device area (repeated 
hot(un)plug of differing DIMMs).

Assume you have 1 GiB range and hotplug a 512 MiB DIMM at offset 256 
MiB. You won't be able to hotplug another 512 MiB DIMM even though we 
reserved space.

My take so far is: if the user wants to do such stuff it should size the 
area (maxmem) much larger or deal with the concequences (not being able 
to hotplug memory).

It usually does not happen in practice ...

> 
> As I sent in an earlier email, users must already comply to the alignment of the host
> memory when plugging pc-dimms, so I'm not sure our value/proposition with all this
> extra code is worth it - the alignment will most likely be forced by the host memory
> backend, so might as well force ourselves in pre_plug().

At least on x86-64, the 2 MiB alignment requirement is handled 
automatically. QEMU_VMALLOC_ALIGN implicitly enforces that.

Maybe RISCV also wants to set QEMU_VMALLOC_ALIGN?

-- 
Cheers,

David / dhildenb

David Hildenbrand <david@redhat.com> writes:

> On 24.05.24 15:14, Daniel Henrique Barboza wrote:
>> 
>> 
>> On 5/21/24 07:56, Björn Töpel wrote:
>>> From: Björn Töpel <bjorn@rivosinc.com>
>>>
>>> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
>>> dynamic resizing of virtual machine memory, and requires proper
>>> hotplugging (add/remove) support to work.
>>>
>>> Add device memory support for RISC-V "virt" machine, and enable
>>> virtio-md-pci with the corresponding missing hotplugging callbacks.
>>>
>>> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
>>> ---
>>>    hw/riscv/Kconfig       |  2 +
>>>    hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>>>    hw/virtio/virtio-mem.c |  5 ++-
>>>    3 files changed, 87 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
>>> index a2030e3a6ff0..08f82dbb681a 100644
>>> --- a/hw/riscv/Kconfig
>>> +++ b/hw/riscv/Kconfig
>>> @@ -56,6 +56,8 @@ config RISCV_VIRT
>>>        select PLATFORM_BUS
>>>        select ACPI
>>>        select ACPI_PCI
>>> +    select VIRTIO_MEM_SUPPORTED
>>> +    select VIRTIO_PMEM_SUPPORTED
>>>    
>>>    config SHAKTI_C
>>>        bool
>>> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>>> index 4fdb66052587..443902f919d2 100644
>>> --- a/hw/riscv/virt.c
>>> +++ b/hw/riscv/virt.c
>>> @@ -53,6 +53,8 @@
>>>    #include "hw/pci-host/gpex.h"
>>>    #include "hw/display/ramfb.h"
>>>    #include "hw/acpi/aml-build.h"
>>> +#include "hw/mem/memory-device.h"
>>> +#include "hw/virtio/virtio-mem-pci.h"
>>>    #include "qapi/qapi-visit-common.h"
>>>    #include "hw/virtio/virtio-iommu.h"
>>>    
>>> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>>>        DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>>>        int i, base_hartid, hart_count;
>>>        int socket_count = riscv_socket_count(machine);
>>> +    hwaddr device_memory_base, device_memory_size;
>>>    
>>>        /* Check socket count limit */
>>>        if (VIRT_SOCKETS_MAX < socket_count) {
>>> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>>>            exit(1);
>>>        }
>>>    
>>> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
>>> +        error_report("unsupported amount of memory slots: %"PRIu64,
>>> +                     machine->ram_slots);
>>> +        exit(EXIT_FAILURE);
>>> +    }
>>> +
>>>        /* Initialize sockets */
>>>        mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
>>>        for (i = 0; i < socket_count; i++) {
>>> @@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
>>>        memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
>>>                                    mask_rom);
>>>    
>>> +    /* device memory */
>>> +    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
>>> +                                  GiB);
>>> +    device_memory_size = machine->maxram_size - machine->ram_size;
>>> +    if (device_memory_size > 0) {
>>> +        /*
>>> +         * Each DIMM is aligned based on the backend's alignment value.
>>> +         * Assume max 1G hugepage alignment per slot.
>>> +         */
>>> +        device_memory_size += machine->ram_slots * GiB;
>> 
>> We don't need to align to 1GiB. This calc can use 2MiB instead (or 4MiB if we're
>> running 32 bits).
>> 
>>> +
>>> +        if (riscv_is_32bit(&s->soc[0])) {
>>> +            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
>>> +                                                          GiB);
>> 
>> Same here - alignment is 2/4 MiB.
>> 
>>> +
>>> +            if (memtop > UINT32_MAX) {
>>> +                error_report("memory exceeds 32-bit limit by %lu bytes",
>>> +                             memtop - UINT32_MAX);
>>> +                exit(EXIT_FAILURE);
>>> +            }
>>> +        }
>>> +
>>> +        if (device_memory_base + device_memory_size < device_memory_size) {
>>> +            error_report("unsupported amount of device memory");
>>> +            exit(EXIT_FAILURE);
>>> +        }
>> 
>> Took another look and found this a bit strange. These are all unsigned vars, so
>> if (unsigned a + unsigned b < unsigned b) will always be 'false'. The compiler is
>> probably cropping this out.
>
> No. Unsigned interger overflow is defined behavior and this is a common 
> check to detect such overflow. tI's consistent with what we do for other 
> architectures.
>
>> 
>> The calc we need to do is to ensure that the extra ram_slots * alignment will fit into
>> the VIRT_DRAM block, i.e. maxram_size + (ram_slots * alignment) < memmap[VIRT_DRAM].size.
>> 
>> 
>> TBH I'm starting to have second thoughts about letting users hotplug whatever they want.
>> It seems cleaner to just force the 2/4 Mb alignment in pre_plug() and be done with it,
>> no need to allocate ram_slots * alignment and doing all these extra checks.
>
> It's worth noting that if user space decides to specify addresses 
> manually, it can mess up everything already. There are other events that 
> can result in fragmentation of the memory device area (repeated 
> hot(un)plug of differing DIMMs).
>
> Assume you have 1 GiB range and hotplug a 512 MiB DIMM at offset 256 
> MiB. You won't be able to hotplug another 512 MiB DIMM even though we 
> reserved space.
>
> My take so far is: if the user wants to do such stuff it should size the 
> area (maxmem) much larger or deal with the concequences (not being able 
> to hotplug memory).
>
> It usually does not happen in practice ...

Daniel/David, again thanks for spending time on the patches.

The reason I picked 1 GiB per slot was because the alignment is also
dependent on the backend AFAIU. Rationale in commit 085f8e88ba73 ("pc:
count in 1Gb hugepage alignment when sizing hotplug-memory container").

What I'm reading from you guys are: Just depend on whatever maxmem says
(modulo 2/4M alignment), and leave at that. I agree that that's much
easier to reason about.

Correct?

>> As I sent in an earlier email, users must already comply to the alignment of the host
>> memory when plugging pc-dimms, so I'm not sure our value/proposition with all this
>> extra code is worth it - the alignment will most likely be forced by the host memory
>> backend, so might as well force ourselves in pre_plug().
>
> At least on x86-64, the 2 MiB alignment requirement is handled 
> automatically. QEMU_VMALLOC_ALIGN implicitly enforces that.
>
> Maybe RISCV also wants to set QEMU_VMALLOC_ALIGN?

I'll look into this for the next rev!


Björn

On 5/27/24 09:03, Björn Töpel wrote:
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 24.05.24 15:14, Daniel Henrique Barboza wrote:
>>>
>>>
>>> On 5/21/24 07:56, Björn Töpel wrote:
>>>> From: Björn Töpel <bjorn@rivosinc.com>
>>>>
>>>> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
>>>> dynamic resizing of virtual machine memory, and requires proper
>>>> hotplugging (add/remove) support to work.
>>>>
>>>> Add device memory support for RISC-V "virt" machine, and enable
>>>> virtio-md-pci with the corresponding missing hotplugging callbacks.
>>>>
>>>> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
>>>> ---
>>>>     hw/riscv/Kconfig       |  2 +
>>>>     hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>>>>     hw/virtio/virtio-mem.c |  5 ++-
>>>>     3 files changed, 87 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
>>>> index a2030e3a6ff0..08f82dbb681a 100644
>>>> --- a/hw/riscv/Kconfig
>>>> +++ b/hw/riscv/Kconfig
>>>> @@ -56,6 +56,8 @@ config RISCV_VIRT
>>>>         select PLATFORM_BUS
>>>>         select ACPI
>>>>         select ACPI_PCI
>>>> +    select VIRTIO_MEM_SUPPORTED
>>>> +    select VIRTIO_PMEM_SUPPORTED
>>>>     
>>>>     config SHAKTI_C
>>>>         bool
>>>> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>>>> index 4fdb66052587..443902f919d2 100644
>>>> --- a/hw/riscv/virt.c
>>>> +++ b/hw/riscv/virt.c
>>>> @@ -53,6 +53,8 @@
>>>>     #include "hw/pci-host/gpex.h"
>>>>     #include "hw/display/ramfb.h"
>>>>     #include "hw/acpi/aml-build.h"
>>>> +#include "hw/mem/memory-device.h"
>>>> +#include "hw/virtio/virtio-mem-pci.h"
>>>>     #include "qapi/qapi-visit-common.h"
>>>>     #include "hw/virtio/virtio-iommu.h"
>>>>     
>>>> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>>>>         DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>>>>         int i, base_hartid, hart_count;
>>>>         int socket_count = riscv_socket_count(machine);
>>>> +    hwaddr device_memory_base, device_memory_size;
>>>>     
>>>>         /* Check socket count limit */
>>>>         if (VIRT_SOCKETS_MAX < socket_count) {
>>>> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>>>>             exit(1);
>>>>         }
>>>>     
>>>> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
>>>> +        error_report("unsupported amount of memory slots: %"PRIu64,
>>>> +                     machine->ram_slots);
>>>> +        exit(EXIT_FAILURE);
>>>> +    }
>>>> +
>>>>         /* Initialize sockets */
>>>>         mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
>>>>         for (i = 0; i < socket_count; i++) {
>>>> @@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
>>>>         memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
>>>>                                     mask_rom);
>>>>     
>>>> +    /* device memory */
>>>> +    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
>>>> +                                  GiB);
>>>> +    device_memory_size = machine->maxram_size - machine->ram_size;
>>>> +    if (device_memory_size > 0) {
>>>> +        /*
>>>> +         * Each DIMM is aligned based on the backend's alignment value.
>>>> +         * Assume max 1G hugepage alignment per slot.
>>>> +         */
>>>> +        device_memory_size += machine->ram_slots * GiB;
>>>
>>> We don't need to align to 1GiB. This calc can use 2MiB instead (or 4MiB if we're
>>> running 32 bits).
>>>
>>>> +
>>>> +        if (riscv_is_32bit(&s->soc[0])) {
>>>> +            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
>>>> +                                                          GiB);
>>>
>>> Same here - alignment is 2/4 MiB.
>>>
>>>> +
>>>> +            if (memtop > UINT32_MAX) {
>>>> +                error_report("memory exceeds 32-bit limit by %lu bytes",
>>>> +                             memtop - UINT32_MAX);
>>>> +                exit(EXIT_FAILURE);
>>>> +            }
>>>> +        }
>>>> +
>>>> +        if (device_memory_base + device_memory_size < device_memory_size) {
>>>> +            error_report("unsupported amount of device memory");
>>>> +            exit(EXIT_FAILURE);
>>>> +        }
>>>
>>> Took another look and found this a bit strange. These are all unsigned vars, so
>>> if (unsigned a + unsigned b < unsigned b) will always be 'false'. The compiler is
>>> probably cropping this out.
>>
>> No. Unsigned interger overflow is defined behavior and this is a common
>> check to detect such overflow. tI's consistent with what we do for other
>> architectures.
>>
>>>
>>> The calc we need to do is to ensure that the extra ram_slots * alignment will fit into
>>> the VIRT_DRAM block, i.e. maxram_size + (ram_slots * alignment) < memmap[VIRT_DRAM].size.
>>>
>>>
>>> TBH I'm starting to have second thoughts about letting users hotplug whatever they want.
>>> It seems cleaner to just force the 2/4 Mb alignment in pre_plug() and be done with it,
>>> no need to allocate ram_slots * alignment and doing all these extra checks.
>>
>> It's worth noting that if user space decides to specify addresses
>> manually, it can mess up everything already. There are other events that
>> can result in fragmentation of the memory device area (repeated
>> hot(un)plug of differing DIMMs).
>>
>> Assume you have 1 GiB range and hotplug a 512 MiB DIMM at offset 256
>> MiB. You won't be able to hotplug another 512 MiB DIMM even though we
>> reserved space.
>>
>> My take so far is: if the user wants to do such stuff it should size the
>> area (maxmem) much larger or deal with the concequences (not being able
>> to hotplug memory).
>>
>> It usually does not happen in practice ...
> 
> Daniel/David, again thanks for spending time on the patches.
> 
> The reason I picked 1 GiB per slot was because the alignment is also
> dependent on the backend AFAIU. Rationale in commit 085f8e88ba73 ("pc:
> count in 1Gb hugepage alignment when sizing hotplug-memory container").
> 
> What I'm reading from you guys are: Just depend on whatever maxmem says
> (modulo 2/4M alignment), and leave at that. I agree that that's much
> easier to reason about.
> 
> Correct?

We could opt for the more conservative approach and keep the 1Gb per dimm to
account for hugepage mem fragmentation that the commit is talking about, assuming
that this scenario is still feasible to happen.

riscv64 can take this extra restriction (i.e. an extra 256GiB RAM just for that)
but I'm afraid this would eradicate hotplug support for riscv32 since it'll never
has enough memory to deal with a spare 1Gb per slot.

I'm aware that you're working in the RISC-V kernel support for memory hotplug, so
you can answer this better than I can: do we care about hugepage support for
riscv32? Assuming we don't, then we could keep 4MiB alignment for riscv32 but do
1GiB for riscv64 to account for this potential hugepage fragmentation.


Thanks,

Daniel

> 
>>> As I sent in an earlier email, users must already comply to the alignment of the host
>>> memory when plugging pc-dimms, so I'm not sure our value/proposition with all this
>>> extra code is worth it - the alignment will most likely be forced by the host memory
>>> backend, so might as well force ourselves in pre_plug().
>>
>> At least on x86-64, the 2 MiB alignment requirement is handled
>> automatically. QEMU_VMALLOC_ALIGN implicitly enforces that.
>>
>> Maybe RISCV also wants to set QEMU_VMALLOC_ALIGN?
> 
> I'll look into this for the next rev!
> 
> 
> Björn

On 5/24/24 12:02, David Hildenbrand wrote:
> On 24.05.24 15:14, Daniel Henrique Barboza wrote:
>>
>>
>> On 5/21/24 07:56, Björn Töpel wrote:
>>> From: Björn Töpel <bjorn@rivosinc.com>
>>>
>>> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
>>> dynamic resizing of virtual machine memory, and requires proper
>>> hotplugging (add/remove) support to work.
>>>
>>> Add device memory support for RISC-V "virt" machine, and enable
>>> virtio-md-pci with the corresponding missing hotplugging callbacks.
>>>
>>> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
>>> ---
>>>    hw/riscv/Kconfig       |  2 +
>>>    hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>>>    hw/virtio/virtio-mem.c |  5 ++-
>>>    3 files changed, 87 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
>>> index a2030e3a6ff0..08f82dbb681a 100644
>>> --- a/hw/riscv/Kconfig
>>> +++ b/hw/riscv/Kconfig
>>> @@ -56,6 +56,8 @@ config RISCV_VIRT
>>>        select PLATFORM_BUS
>>>        select ACPI
>>>        select ACPI_PCI
>>> +    select VIRTIO_MEM_SUPPORTED
>>> +    select VIRTIO_PMEM_SUPPORTED
>>>    config SHAKTI_C
>>>        bool
>>> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>>> index 4fdb66052587..443902f919d2 100644
>>> --- a/hw/riscv/virt.c
>>> +++ b/hw/riscv/virt.c
>>> @@ -53,6 +53,8 @@
>>>    #include "hw/pci-host/gpex.h"
>>>    #include "hw/display/ramfb.h"
>>>    #include "hw/acpi/aml-build.h"
>>> +#include "hw/mem/memory-device.h"
>>> +#include "hw/virtio/virtio-mem-pci.h"
>>>    #include "qapi/qapi-visit-common.h"
>>>    #include "hw/virtio/virtio-iommu.h"
>>> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>>>        DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>>>        int i, base_hartid, hart_count;
>>>        int socket_count = riscv_socket_count(machine);
>>> +    hwaddr device_memory_base, device_memory_size;
>>>        /* Check socket count limit */
>>>        if (VIRT_SOCKETS_MAX < socket_count) {
>>> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>>>            exit(1);
>>>        }
>>> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
>>> +        error_report("unsupported amount of memory slots: %"PRIu64,
>>> +                     machine->ram_slots);
>>> +        exit(EXIT_FAILURE);
>>> +    }
>>> +
>>>        /* Initialize sockets */
>>>        mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
>>>        for (i = 0; i < socket_count; i++) {
>>> @@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
>>>        memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
>>>                                    mask_rom);
>>> +    /* device memory */
>>> +    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
>>> +                                  GiB);
>>> +    device_memory_size = machine->maxram_size - machine->ram_size;
>>> +    if (device_memory_size > 0) {
>>> +        /*
>>> +         * Each DIMM is aligned based on the backend's alignment value.
>>> +         * Assume max 1G hugepage alignment per slot.
>>> +         */
>>> +        device_memory_size += machine->ram_slots * GiB;
>>
>> We don't need to align to 1GiB. This calc can use 2MiB instead (or 4MiB if we're
>> running 32 bits).
>>
>>> +
>>> +        if (riscv_is_32bit(&s->soc[0])) {
>>> +            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
>>> +                                                          GiB);
>>
>> Same here - alignment is 2/4 MiB.
>>
>>> +
>>> +            if (memtop > UINT32_MAX) {
>>> +                error_report("memory exceeds 32-bit limit by %lu bytes",
>>> +                             memtop - UINT32_MAX);
>>> +                exit(EXIT_FAILURE);
>>> +            }
>>> +        }
>>> +
>>> +        if (device_memory_base + device_memory_size < device_memory_size) {
>>> +            error_report("unsupported amount of device memory");
>>> +            exit(EXIT_FAILURE);
>>> +        }
>>
>> Took another look and found this a bit strange. These are all unsigned vars, so
>> if (unsigned a + unsigned b < unsigned b) will always be 'false'. The compiler is
>> probably cropping this out.
> 
> No. Unsigned interger overflow is defined behavior and this is a common check to detect such overflow. tI's consistent with what we do for other architectures.
>

Oh, ok. We're so far away from UINT64_MAX that it didn't occur to me doing an overflow
check here. Fair enough.

  
>>
>> The calc we need to do is to ensure that the extra ram_slots * alignment will fit into
>> the VIRT_DRAM block, i.e. maxram_size + (ram_slots * alignment) < memmap[VIRT_DRAM].size.
>>
>>
>> TBH I'm starting to have second thoughts about letting users hotplug whatever they want.
>> It seems cleaner to just force the 2/4 Mb alignment in pre_plug() and be done with it,
>> no need to allocate ram_slots * alignment and doing all these extra checks.
> 
> It's worth noting that if user space decides to specify addresses manually, it can mess up everything already. There are other events that can result in fragmentation of the memory device area (repeated hot(un)plug of differing DIMMs).
> 
> Assume you have 1 GiB range and hotplug a 512 MiB DIMM at offset 256 MiB. You won't be able to hotplug another 512 MiB DIMM even though we reserved space.
> 
> My take so far is: if the user wants to do such stuff it should size the area (maxmem) much larger or deal with the concequences (not being able to hotplug memory).
> 
> It usually does not happen in practice ...
> 

I wonder if we should forbid users from removing memory that is 'out of place', i.e. users
should always remove pc-dimms in LIFO order. Usually this kind of control is done by
management, e.g. libvirt, but if we're not sure we'll keep consistency during memory
unplugs ...

>>
>> As I sent in an earlier email, users must already comply to the alignment of the host
>> memory when plugging pc-dimms, so I'm not sure our value/proposition with all this
>> extra code is worth it - the alignment will most likely be forced by the host memory
>> backend, so might as well force ourselves in pre_plug().
> 
> At least on x86-64, the 2 MiB alignment requirement is handled automatically. QEMU_VMALLOC_ALIGN implicitly enforces that.
> 
> Maybe RISCV also wants to set QEMU_VMALLOC_ALIGN?

Might be a good idea to experiment.



Thanks,


Daniel

> 

> 
> I wonder if we should forbid users from removing memory that is 'out of place', 
> i.e. users
> should always remove pc-dimms in LIFO order. Usually this kind of control is 
> done by
> management, e.g. libvirt, but if we're not sure we'll keep consistency during 
> memory
> unplugs ...

I really don't think we should do any of that. ;)

-- 
Thanks,

David / dhildenb

On 5/21/24 07:56, Björn Töpel wrote:
> From: Björn Töpel <bjorn@rivosinc.com>
> 
> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
> dynamic resizing of virtual machine memory, and requires proper
> hotplugging (add/remove) support to work.
> 
> Add device memory support for RISC-V "virt" machine, and enable
> virtio-md-pci with the corresponding missing hotplugging callbacks.
> 
> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
> ---
>   hw/riscv/Kconfig       |  2 +
>   hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>   hw/virtio/virtio-mem.c |  5 ++-
>   3 files changed, 87 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
> index a2030e3a6ff0..08f82dbb681a 100644
> --- a/hw/riscv/Kconfig
> +++ b/hw/riscv/Kconfig
> @@ -56,6 +56,8 @@ config RISCV_VIRT
>       select PLATFORM_BUS
>       select ACPI
>       select ACPI_PCI
> +    select VIRTIO_MEM_SUPPORTED
> +    select VIRTIO_PMEM_SUPPORTED
>   
>   config SHAKTI_C
>       bool
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index 4fdb66052587..443902f919d2 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -53,6 +53,8 @@
>   #include "hw/pci-host/gpex.h"
>   #include "hw/display/ramfb.h"
>   #include "hw/acpi/aml-build.h"
> +#include "hw/mem/memory-device.h"
> +#include "hw/virtio/virtio-mem-pci.h"
>   #include "qapi/qapi-visit-common.h"
>   #include "hw/virtio/virtio-iommu.h"
>   
> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>       DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>       int i, base_hartid, hart_count;
>       int socket_count = riscv_socket_count(machine);
> +    hwaddr device_memory_base, device_memory_size;
>   
>       /* Check socket count limit */
>       if (VIRT_SOCKETS_MAX < socket_count) {
> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>           exit(1);
>       }
>   
> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
> +        error_report("unsupported amount of memory slots: %"PRIu64,
> +                     machine->ram_slots);

Let's also add the maximum amount allowed in this message, e.g. this error:

$ (...) -m 2G,slots=512,maxmem=8G
qemu-system-riscv64: unsupported amount of memory slots: 512

could be something like:

qemu-system-riscv64: unsupported amount of memory slots (512), maximum amount: 256


LGTM otherwise. Thanks,


Daniel



> +        exit(EXIT_FAILURE);
> +    }
> +
>       /* Initialize sockets */
>       mmio_irqchip = virtio_irqchip = pcie_irqchip = NULL;
>       for (i = 0; i < socket_count; i++) {
> @@ -1553,6 +1562,37 @@ static void virt_machine_init(MachineState *machine)
>       memory_region_add_subregion(system_memory, memmap[VIRT_MROM].base,
>                                   mask_rom);
>   
> +    /* device memory */
> +    device_memory_base = ROUND_UP(s->memmap[VIRT_DRAM].base + machine->ram_size,
> +                                  GiB);
> +    device_memory_size = machine->maxram_size - machine->ram_size;
> +    if (device_memory_size > 0) {
> +        /*
> +         * Each DIMM is aligned based on the backend's alignment value.
> +         * Assume max 1G hugepage alignment per slot.
> +         */
> +        device_memory_size += machine->ram_slots * GiB;
> +
> +        if (riscv_is_32bit(&s->soc[0])) {
> +            hwaddr memtop = device_memory_base + ROUND_UP(device_memory_size,
> +                                                          GiB);
> +
> +            if (memtop > UINT32_MAX) {
> +                error_report("memory exceeds 32-bit limit by %lu bytes",
> +                             memtop - UINT32_MAX);
> +                exit(EXIT_FAILURE);
> +            }
> +        }
> +
> +        if (device_memory_base + device_memory_size < device_memory_size) {
> +            error_report("unsupported amount of device memory");
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        machine_memory_devices_init(machine, device_memory_base,
> +                                    device_memory_size);
> +    }
> +>       /*
>        * Init fw_cfg. Must be done before riscv_load_fdt, otherwise the
>        * device tree cannot be altered and we get FDT_ERR_NOSPACE.
> @@ -1712,12 +1752,21 @@ static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
>       MachineClass *mc = MACHINE_GET_CLASS(machine);
>   
>       if (device_is_dynamic_sysbus(mc, dev) ||
> -        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
> +        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI) ||
> +        object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
>           return HOTPLUG_HANDLER(machine);
>       }
>       return NULL;
>   }
>   
> +static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
> +                                            DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_pre_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
> +    }
> +}
> +
>   static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>                                           DeviceState *dev, Error **errp)
>   {
> @@ -1735,6 +1784,35 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>       if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_IOMMU_PCI)) {
>           create_fdt_virtio_iommu(s, pci_get_bdf(PCI_DEVICE(dev)));
>       }
> +
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_plug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
> +    }
> +}
> +
> +static void virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
> +                                                  DeviceState *dev,
> +                                                  Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_unplug_request(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev),
> +                                     errp);
> +    } else {
> +        error_setg(errp,
> +                   "device unplug request for unsupported device type: %s",
> +                   object_get_typename(OBJECT(dev)));
> +    }
> +}
> +
> +static void virt_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
> +                                          DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
> +        virtio_md_pci_unplug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
> +    } else {
> +        error_setg(errp, "virt: device unplug for unsupported device"
> +                   " type: %s", object_get_typename(OBJECT(dev)));
> +    }
>   }
>   
>   static void virt_machine_class_init(ObjectClass *oc, void *data)
> @@ -1757,7 +1835,10 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
>       assert(!mc->get_hotplug_handler);
>       mc->get_hotplug_handler = virt_machine_get_hotplug_handler;
>   
> +    hc->pre_plug = virt_machine_device_pre_plug_cb;
>       hc->plug = virt_machine_device_plug_cb;
> +    hc->unplug_request = virt_machine_device_unplug_request_cb;
> +    hc->unplug = virt_machine_device_unplug_cb;
>   
>       machine_class_allow_dynamic_sysbus_dev(mc, TYPE_RAMFB_DEVICE);
>   #ifdef CONFIG_TPM
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index ffd119ebacb7..6636e5e1089c 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -51,7 +51,8 @@ static uint32_t virtio_mem_default_thp_size(void)
>   {
>       uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
>   
> -#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
> +#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__) \
> +    || defined(__riscv__)
>       default_thp_size = 2 * MiB;
>   #elif defined(__aarch64__)
>       if (qemu_real_host_page_size() == 4 * KiB) {
> @@ -161,7 +162,7 @@ static bool virtio_mem_has_shared_zeropage(RAMBlock *rb)
>    * necessary (as the section size can change). But it's more likely that the
>    * section size will rather get smaller and not bigger over time.
>    */
> -#if defined(TARGET_X86_64) || defined(TARGET_I386)
> +#if defined(TARGET_X86_64) || defined(TARGET_I386)  || defined(TARGET_RISCV)
>   #define VIRTIO_MEM_USABLE_EXTENT (2 * (128 * MiB))
>   #elif defined(TARGET_ARM)
>   #define VIRTIO_MEM_USABLE_EXTENT (2 * (512 * MiB))

Daniel Henrique Barboza <dbarboza@ventanamicro.com> writes:

> On 5/21/24 07:56, Björn Töpel wrote:
>> From: Björn Töpel <bjorn@rivosinc.com>
>> 
>> Virtio-based memory devices (virtio-mem/virtio-pmem) allows for
>> dynamic resizing of virtual machine memory, and requires proper
>> hotplugging (add/remove) support to work.
>> 
>> Add device memory support for RISC-V "virt" machine, and enable
>> virtio-md-pci with the corresponding missing hotplugging callbacks.
>> 
>> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
>> ---
>>   hw/riscv/Kconfig       |  2 +
>>   hw/riscv/virt.c        | 83 +++++++++++++++++++++++++++++++++++++++++-
>>   hw/virtio/virtio-mem.c |  5 ++-
>>   3 files changed, 87 insertions(+), 3 deletions(-)
>> 
>> diff --git a/hw/riscv/Kconfig b/hw/riscv/Kconfig
>> index a2030e3a6ff0..08f82dbb681a 100644
>> --- a/hw/riscv/Kconfig
>> +++ b/hw/riscv/Kconfig
>> @@ -56,6 +56,8 @@ config RISCV_VIRT
>>       select PLATFORM_BUS
>>       select ACPI
>>       select ACPI_PCI
>> +    select VIRTIO_MEM_SUPPORTED
>> +    select VIRTIO_PMEM_SUPPORTED
>>   
>>   config SHAKTI_C
>>       bool
>> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>> index 4fdb66052587..443902f919d2 100644
>> --- a/hw/riscv/virt.c
>> +++ b/hw/riscv/virt.c
>> @@ -53,6 +53,8 @@
>>   #include "hw/pci-host/gpex.h"
>>   #include "hw/display/ramfb.h"
>>   #include "hw/acpi/aml-build.h"
>> +#include "hw/mem/memory-device.h"
>> +#include "hw/virtio/virtio-mem-pci.h"
>>   #include "qapi/qapi-visit-common.h"
>>   #include "hw/virtio/virtio-iommu.h"
>>   
>> @@ -1407,6 +1409,7 @@ static void virt_machine_init(MachineState *machine)
>>       DeviceState *mmio_irqchip, *virtio_irqchip, *pcie_irqchip;
>>       int i, base_hartid, hart_count;
>>       int socket_count = riscv_socket_count(machine);
>> +    hwaddr device_memory_base, device_memory_size;
>>   
>>       /* Check socket count limit */
>>       if (VIRT_SOCKETS_MAX < socket_count) {
>> @@ -1420,6 +1423,12 @@ static void virt_machine_init(MachineState *machine)
>>           exit(1);
>>       }
>>   
>> +    if (machine->ram_slots > ACPI_MAX_RAM_SLOTS) {
>> +        error_report("unsupported amount of memory slots: %"PRIu64,
>> +                     machine->ram_slots);
>
> Let's also add the maximum amount allowed in this message, e.g. this error:
>
> $ (...) -m 2G,slots=512,maxmem=8G
> qemu-system-riscv64: unsupported amount of memory slots: 512
>
> could be something like:
>
> qemu-system-riscv64: unsupported amount of memory slots (512), maximum amount: 256
>
>
> LGTM otherwise. Thanks,

Thanks for getting back!

Sure! I'll fix this in the next rev.


Björn