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Tsirkin" , Juraj Marcin , Peter Maydell Subject: [PATCH v1] virtio-mem: unplug memory only during system resets, not device resets Date: Fri, 25 Oct 2024 12:41:03 +0200 Message-ID: <20241025104103.342188-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.263, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1.697, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1729852942864116600 Content-Type: text/plain; charset="utf-8" We recently converted from the LegacyReset to the new reset framework in commit c009a311e939 ("virtio-mem: Use new Resettable framework instead of LegacyReset") to be able to use the ResetType to filter out wakeup resets. However, this change had an undesired implications: as we override the Resettable interface methods in VirtIOMEMClass, the reset handler will not only get called during system resets (i.e., qemu_devices_reset()) but also during any direct or indirect device rests (e.g., device_cold_reset()). Further, we might now receive two reset callbacks during qemu_devices_reset(), first when reset by a parent and later when reset directly. The memory state of virtio-mem devices is rather special: it's supposed to be persistent/unchanged during most resets (similar to resetting a hard disk will not destroy the data), unless actually cold-resetting the whole system (different to a hard disk where a reboot will not destroy the data): ripping out system RAM is something guest OSes don't particularly enjoy, but we want to detect when rebooting to an OS that does not support virtio-mem and wouldn't be able to detect+use the memory -- and we want to force-defragment hotplugged memory to also shrink the usable device memory region. So we rally want to catch system resets to do that. On supported targets (e.g., x86), getting a cold reset on the device/parent triggers is not that easy (but looks like PCI code might trigger it), so this implication went unnoticed. However, with upcoming s390x support it is problematic: during kdump, s390x triggers a subsystem reset, ending up in s390_machine_reset() and calling only subsystem_reset() instead of qemu_devices_reset() -- because it's not a full system reset. In subsystem_reset(), s390x performs a device_cold_reset() of any TYPE_VIRTUAL_CSS_BRIDGE device, which ends up resetting all children, including the virtio-mem device. Consequently, we wrongly detect a system reset and unplug all device memory, resulting in hotplugged memory not getting included in the crash dump -- undesired. We really must not mess with hotplugged memory state during simple device resets. To fix, create+register a new reset object that will only get triggered during qemu_devices_reset() calls, but not during any other resets as it is logically not the child of any other object. Cc: "Michael S. Tsirkin" Cc: Juraj Marcin Cc: Peter Maydell Signed-off-by: David Hildenbrand Acked-by: Michael S. Tsirkin --- hw/virtio/virtio-mem.c | 103 +++++++++++++++++++++++---------- include/hw/virtio/virtio-mem.h | 12 +++- 2 files changed, 83 insertions(+), 32 deletions(-) diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c index ae1e81d7ba..08e0e9da1c 100644 --- a/hw/virtio/virtio-mem.c +++ b/hw/virtio/virtio-mem.c @@ -956,6 +956,7 @@ static void virtio_mem_device_realize(DeviceState *dev,= Error **errp) VirtIOMEM *vmem =3D VIRTIO_MEM(dev); uint64_t page_size; RAMBlock *rb; + Object *obj; int ret; =20 if (!vmem->memdev) { @@ -1121,7 +1122,28 @@ static void virtio_mem_device_realize(DeviceState *d= ev, Error **errp) vmstate_register_any(VMSTATE_IF(vmem), &vmstate_virtio_mem_device_early, vmem); } - qemu_register_resettable(OBJECT(vmem)); + + /* + * We only want to unplug all memory to start with a clean slate when + * it is safe for the guest -- during system resets that call + * qemu_devices_reset(). + * + * We'll filter out selected qemu_devices_reset() calls used for other + * purposes, like resetting all devices during wakeup from suspend on + * x86 based on the reset type passed to qemu_devices_reset(). + * + * Unplugging all memory during simple device resets can result in the= VM + * unexpectedly losing RAM, corrupting VM state. + * + * Simple device resets (or resets triggered by getting a parent device + * reset) must not change the state of plugged memory blocks. Therefor= e, + * we need a dedicated reset object that only gets called during + * qemu_devices_reset(). + */ + obj =3D object_new(TYPE_VIRTIO_MEM_SYSTEM_RESET); + vmem->system_reset =3D VIRTIO_MEM_SYSTEM_RESET(obj); + vmem->system_reset->vmem =3D vmem; + qemu_register_resettable(obj); =20 /* * Set ourselves as RamDiscardManager before the plug handler maps the @@ -1141,7 +1163,10 @@ static void virtio_mem_device_unrealize(DeviceState = *dev) * found via an address space anymore. Unset ourselves. */ memory_region_set_ram_discard_manager(&vmem->memdev->mr, NULL); - qemu_unregister_resettable(OBJECT(vmem)); + + qemu_unregister_resettable(OBJECT(vmem->system_reset)); + object_unref(OBJECT(vmem->system_reset)); + if (vmem->early_migration) { vmstate_unregister(VMSTATE_IF(vmem), &vmstate_virtio_mem_device_ea= rly, vmem); @@ -1841,38 +1866,12 @@ static void virtio_mem_unplug_request_check(VirtIOM= EM *vmem, Error **errp) } } =20 -static ResettableState *virtio_mem_get_reset_state(Object *obj) -{ - VirtIOMEM *vmem =3D VIRTIO_MEM(obj); - return &vmem->reset_state; -} - -static void virtio_mem_system_reset_hold(Object *obj, ResetType type) -{ - VirtIOMEM *vmem =3D VIRTIO_MEM(obj); - - /* - * When waking up from standby/suspend-to-ram, do not unplug any memor= y. - */ - if (type =3D=3D RESET_TYPE_WAKEUP) { - return; - } - - /* - * During usual resets, we will unplug all memory and shrink the usable - * region size. This is, however, not possible in all scenarios. Then, - * the guest has to deal with this manually (VIRTIO_MEM_REQ_UNPLUG_ALL= ). - */ - virtio_mem_unplug_all(vmem); -} - static void virtio_mem_class_init(ObjectClass *klass, void *data) { DeviceClass *dc =3D DEVICE_CLASS(klass); VirtioDeviceClass *vdc =3D VIRTIO_DEVICE_CLASS(klass); VirtIOMEMClass *vmc =3D VIRTIO_MEM_CLASS(klass); RamDiscardManagerClass *rdmc =3D RAM_DISCARD_MANAGER_CLASS(klass); - ResettableClass *rc =3D RESETTABLE_CLASS(klass); =20 device_class_set_props(dc, virtio_mem_properties); dc->vmsd =3D &vmstate_virtio_mem; @@ -1899,9 +1898,6 @@ static void virtio_mem_class_init(ObjectClass *klass,= void *data) rdmc->replay_discarded =3D virtio_mem_rdm_replay_discarded; rdmc->register_listener =3D virtio_mem_rdm_register_listener; rdmc->unregister_listener =3D virtio_mem_rdm_unregister_listener; - - rc->get_state =3D virtio_mem_get_reset_state; - rc->phases.hold =3D virtio_mem_system_reset_hold; } =20 static const TypeInfo virtio_mem_info =3D { @@ -1924,3 +1920,48 @@ static void virtio_register_types(void) } =20 type_init(virtio_register_types) + +OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(VirtioMemSystemReset, virtio_mem= _system_reset, VIRTIO_MEM_SYSTEM_RESET, OBJECT, { TYPE_RESETTABLE_INTERFACE= }, { }) + +static void virtio_mem_system_reset_init(Object *obj) +{ +} + +static void virtio_mem_system_reset_finalize(Object *obj) +{ +} + +static ResettableState *virtio_mem_system_reset_get_state(Object *obj) +{ + VirtioMemSystemReset *vmem_reset =3D VIRTIO_MEM_SYSTEM_RESET(obj); + + return &vmem_reset->reset_state; +} + +static void virtio_mem_system_reset_hold(Object *obj, ResetType type) +{ + VirtioMemSystemReset *vmem_reset =3D VIRTIO_MEM_SYSTEM_RESET(obj); + VirtIOMEM *vmem =3D vmem_reset->vmem; + + /* + * When waking up from standby/suspend-to-ram, do not unplug any memor= y. + */ + if (type =3D=3D RESET_TYPE_WAKEUP) { + return; + } + + /* + * During usual resets, we will unplug all memory and shrink the usable + * region size. This is, however, not possible in all scenarios. Then, + * the guest has to deal with this manually (VIRTIO_MEM_REQ_UNPLUG_ALL= ). + */ + virtio_mem_unplug_all(vmem); +} + +static void virtio_mem_system_reset_class_init(ObjectClass *klass, void *d= ata) +{ + ResettableClass *rc =3D RESETTABLE_CLASS(klass); + + rc->get_state =3D virtio_mem_system_reset_get_state; + rc->phases.hold =3D virtio_mem_system_reset_hold; +} diff --git a/include/hw/virtio/virtio-mem.h b/include/hw/virtio/virtio-mem.h index a1af144c28..abde1c4101 100644 --- a/include/hw/virtio/virtio-mem.h +++ b/include/hw/virtio/virtio-mem.h @@ -25,6 +25,10 @@ OBJECT_DECLARE_TYPE(VirtIOMEM, VirtIOMEMClass, VIRTIO_MEM) =20 +#define TYPE_VIRTIO_MEM_SYSTEM_RESET "virtio-mem-system-reset" + +OBJECT_DECLARE_SIMPLE_TYPE(VirtioMemSystemReset, VIRTIO_MEM_SYSTEM_RESET) + #define VIRTIO_MEM_MEMDEV_PROP "memdev" #define VIRTIO_MEM_NODE_PROP "node" #define VIRTIO_MEM_SIZE_PROP "size" @@ -117,8 +121,14 @@ struct VirtIOMEM { /* listeners to notify on plug/unplug activity. */ QLIST_HEAD(, RamDiscardListener) rdl_list; =20 - /* State of the resettable container */ + /* Catch system resets -> qemu_devices_reset() only. */ + VirtioMemSystemReset *system_reset; +}; + +struct VirtioMemSystemReset { + Object parent; ResettableState reset_state; + VirtIOMEM *vmem; }; =20 struct VirtIOMEMClass { --=20 2.46.1