xen/riscv: introduce vtimer related things

[PATCH v2 02/16] xen/riscv: implement arch_vcpu_{create,destroy}()

Posted by Oleksii Kurochko 2 weeks, 3 days ago

Introduce architecture-specific functions to create and destroy VCPUs.
Note that arch_vcpu_create() currently returns -EOPNOTSUPP, as the virtual
timer and interrupt controller are not yet implemented.

As part of this change, add continue_new_vcpu(), which will be used after
the first context_switch() of a new vCPU. Since this functionality is not
yet implemented, continue_new_vcpu() is currently provided as a stub.

Update the STACK_SIZE definition and introduce STACK_ORDER (to align with
other architectures) for allocating the vCPU stack.

Introduce struct cpu_info to store per-vCPU state that lives at the top
of the vCPU's stack.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
Changes in v2:
 - Drop BUILD_BUG_ON() in arch_vcpu_create() as a check isn't very useful.
 - Use vzalloc() instead of alloc_xenheap_page() to use the larger domheap to
   allocate vCPU's stack.
 - Drop printk() inside arch_vcpu_create() to not have potential big noise
   in console as it could be that an amount of vCPUs is pretty big.
 - Use XVFREE() instead of free_xenheap_pages() as vCPU's stack allocation
   happens with a usage of vzalloc() now.
 - Drop stack field as it is enough to have only cpu_info as stack pointer
   could be calculated based on cpu_info.
 - Drop cast when v.arch.cpu_info is inialized as it is not necessary
        to have it.
 - Drop memset() for arch.cpu_info() as it is enough to have vzalloc().
---
 xen/arch/riscv/Makefile              |  1 +
 xen/arch/riscv/domain.c              | 59 ++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/config.h  |  3 +-
 xen/arch/riscv/include/asm/current.h |  6 +++
 xen/arch/riscv/include/asm/domain.h  |  2 +
 xen/arch/riscv/stubs.c               | 10 -----
 6 files changed, 70 insertions(+), 11 deletions(-)
 create mode 100644 xen/arch/riscv/domain.c

diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index 87c1148b0010..8863d4b15605 100644
--- a/xen/arch/riscv/Makefile
+++ b/xen/arch/riscv/Makefile
@@ -1,5 +1,6 @@
 obj-y += aplic.o
 obj-y += cpufeature.o
+obj-y += domain.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-y += entry.o
 obj-y += imsic.o
diff --git a/xen/arch/riscv/domain.c b/xen/arch/riscv/domain.c
new file mode 100644
index 000000000000..9c546267881b
--- /dev/null
+++ b/xen/arch/riscv/domain.c
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/init.h>
+#include <xen/mm.h>
+#include <xen/sched.h>
+#include <xen/vmap.h>
+
+static void continue_new_vcpu(struct vcpu *prev)
+{
+    BUG_ON("unimplemented\n");
+}
+
+static void __init __maybe_unused build_assertions(void)
+{
+    /*
+     * Enforce the requirement documented in struct cpu_info that
+     * guest_cpu_user_regs must be the first field.
+     */
+    BUILD_BUG_ON(offsetof(struct cpu_info, guest_cpu_user_regs) != 0);
+}
+
+int arch_vcpu_create(struct vcpu *v)
+{
+    int rc = 0;
+    void *stack = vzalloc(STACK_SIZE);
+
+    if ( !stack )
+        return -ENOMEM;
+
+    v->arch.cpu_info = stack + STACK_SIZE - sizeof(struct cpu_info);
+    memset(v->arch.cpu_info, 0, sizeof(*v->arch.cpu_info));
+
+    v->arch.xen_saved_context.sp = (register_t)v->arch.cpu_info;
+    v->arch.xen_saved_context.ra = (register_t)continue_new_vcpu;
+
+    /* Idle VCPUs don't need the rest of this setup */
+    if ( is_idle_vcpu(v) )
+        return rc;
+
+    /*
+     * As the vtimer and interrupt controller (IC) are not yet implemented,
+     * return an error.
+     *
+     * TODO: Drop this once the vtimer and IC are implemented.
+     */
+    rc = -EOPNOTSUPP;
+    goto fail;
+
+    return rc;
+
+ fail:
+    arch_vcpu_destroy(v);
+    return rc;
+}
+
+void arch_vcpu_destroy(struct vcpu *v)
+{
+    vfree((char *)v->arch.cpu_info + sizeof(struct cpu_info));
+}
diff --git a/xen/arch/riscv/include/asm/config.h b/xen/arch/riscv/include/asm/config.h
index 1e08d3bf78be..86a95df018b5 100644
--- a/xen/arch/riscv/include/asm/config.h
+++ b/xen/arch/riscv/include/asm/config.h
@@ -143,7 +143,8 @@
 
 #define SMP_CACHE_BYTES (1 << 6)
 
-#define STACK_SIZE PAGE_SIZE
+#define STACK_ORDER 3
+#define STACK_SIZE (PAGE_SIZE << STACK_ORDER)
 
 #define IDENT_AREA_SIZE 64
 
diff --git a/xen/arch/riscv/include/asm/current.h b/xen/arch/riscv/include/asm/current.h
index 0c3ea70c2ec8..58c9f1506b7c 100644
--- a/xen/arch/riscv/include/asm/current.h
+++ b/xen/arch/riscv/include/asm/current.h
@@ -21,6 +21,12 @@ struct pcpu_info {
 /* tp points to one of these */
 extern struct pcpu_info pcpu_info[NR_CPUS];
 
+/* Per-VCPU state that lives at the top of the stack */
+struct cpu_info {
+    /* This should be the first member. */
+    struct cpu_user_regs guest_cpu_user_regs;
+};
+
 #define set_processor_id(id)    do { \
     tp->processor_id = (id);         \
 } while (0)
diff --git a/xen/arch/riscv/include/asm/domain.h b/xen/arch/riscv/include/asm/domain.h
index 0d9b4c4b525e..ec7786c76199 100644
--- a/xen/arch/riscv/include/asm/domain.h
+++ b/xen/arch/riscv/include/asm/domain.h
@@ -49,6 +49,8 @@ struct arch_vcpu
         register_t ra;
     } xen_saved_context;
 
+    struct cpu_info *cpu_info;
+
     /* CSRs */
     register_t hedeleg;
     register_t hideleg;
diff --git a/xen/arch/riscv/stubs.c b/xen/arch/riscv/stubs.c
index 29bdb65afbdf..9e30a9a3b50b 100644
--- a/xen/arch/riscv/stubs.c
+++ b/xen/arch/riscv/stubs.c
@@ -121,16 +121,6 @@ void dump_pageframe_info(struct domain *d)
     BUG_ON("unimplemented");
 }
 
-int arch_vcpu_create(struct vcpu *v)
-{
-    BUG_ON("unimplemented");
-}
-
-void arch_vcpu_destroy(struct vcpu *v)
-{
-    BUG_ON("unimplemented");
-}
-
 void vcpu_switch_to_aarch64_mode(struct vcpu *v)
 {
     BUG_ON("unimplemented");
-- 
2.52.0

Re: [PATCH v2 02/16] xen/riscv: implement arch_vcpu_{create,destroy}()

Posted by Teddy Astie 2 weeks, 3 days ago

Hello,

Le 22/01/2026 à 17:49, Oleksii Kurochko a écrit :
> Introduce architecture-specific functions to create and destroy VCPUs.
> Note that arch_vcpu_create() currently returns -EOPNOTSUPP, as the virtual
> timer and interrupt controller are not yet implemented.
> 
> As part of this change, add continue_new_vcpu(), which will be used after
> the first context_switch() of a new vCPU. Since this functionality is not
> yet implemented, continue_new_vcpu() is currently provided as a stub.
> 
> Update the STACK_SIZE definition and introduce STACK_ORDER (to align with
> other architectures) for allocating the vCPU stack.
> 
> Introduce struct cpu_info to store per-vCPU state that lives at the top
> of the vCPU's stack.
> 
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> ---
> Changes in v2:
>   - Drop BUILD_BUG_ON() in arch_vcpu_create() as a check isn't very useful.
>   - Use vzalloc() instead of alloc_xenheap_page() to use the larger domheap to
>     allocate vCPU's stack.
>   - Drop printk() inside arch_vcpu_create() to not have potential big noise
>     in console as it could be that an amount of vCPUs is pretty big.
>   - Use XVFREE() instead of free_xenheap_pages() as vCPU's stack allocation
>     happens with a usage of vzalloc() now.
>   - Drop stack field as it is enough to have only cpu_info as stack pointer
>     could be calculated based on cpu_info.
>   - Drop cast when v.arch.cpu_info is inialized as it is not necessary
>          to have it.
>   - Drop memset() for arch.cpu_info() as it is enough to have vzalloc().
> ---
>   xen/arch/riscv/Makefile              |  1 +
>   xen/arch/riscv/domain.c              | 59 ++++++++++++++++++++++++++++
>   xen/arch/riscv/include/asm/config.h  |  3 +-
>   xen/arch/riscv/include/asm/current.h |  6 +++
>   xen/arch/riscv/include/asm/domain.h  |  2 +
>   xen/arch/riscv/stubs.c               | 10 -----
>   6 files changed, 70 insertions(+), 11 deletions(-)
>   create mode 100644 xen/arch/riscv/domain.c
> 
> diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
> index 87c1148b0010..8863d4b15605 100644
> --- a/xen/arch/riscv/Makefile
> +++ b/xen/arch/riscv/Makefile
> @@ -1,5 +1,6 @@
>   obj-y += aplic.o
>   obj-y += cpufeature.o
> +obj-y += domain.o
>   obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
>   obj-y += entry.o
>   obj-y += imsic.o
> diff --git a/xen/arch/riscv/domain.c b/xen/arch/riscv/domain.c
> new file mode 100644
> index 000000000000..9c546267881b
> --- /dev/null
> +++ b/xen/arch/riscv/domain.c
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <xen/init.h>
> +#include <xen/mm.h>
> +#include <xen/sched.h>
> +#include <xen/vmap.h>
> +
> +static void continue_new_vcpu(struct vcpu *prev)
> +{
> +    BUG_ON("unimplemented\n");
> +}
> +
> +static void __init __maybe_unused build_assertions(void)
> +{
> +    /*
> +     * Enforce the requirement documented in struct cpu_info that
> +     * guest_cpu_user_regs must be the first field.
> +     */
> +    BUILD_BUG_ON(offsetof(struct cpu_info, guest_cpu_user_regs) != 0);
> +}
> +
> +int arch_vcpu_create(struct vcpu *v)
> +{
> +    int rc = 0;
> +    void *stack = vzalloc(STACK_SIZE);
> +

Are there alignment constraints for the stack ?

> +    if ( !stack )
> +        return -ENOMEM;
> +
> +    v->arch.cpu_info = stack + STACK_SIZE - sizeof(struct cpu_info);
> +    memset(v->arch.cpu_info, 0, sizeof(*v->arch.cpu_info));
> +

Given that vzalloc ensures that the memory is cleared, you don't need to 
clear it another time.

> +    v->arch.xen_saved_context.sp = (register_t)v->arch.cpu_info;
> +    v->arch.xen_saved_context.ra = (register_t)continue_new_vcpu;
> +

You probably also want to set the first parameter of continue_new_vcpu 
(struct vcpu *prev), or otherwise I don't think we want the "prev" 
parameter in continue_new_vcpu if it's always going to be 0.

IIRC continue_new_vcpu is only meant to bootstrap the new vCPU, not just 
perform a context switch to it.

> +    /* Idle VCPUs don't need the rest of this setup */
> +    if ( is_idle_vcpu(v) )
> +        return rc;
> +
> +    /*
> +     * As the vtimer and interrupt controller (IC) are not yet implemented,
> +     * return an error.
> +     *
> +     * TODO: Drop this once the vtimer and IC are implemented.
> +     */
> +    rc = -EOPNOTSUPP;
> +    goto fail;
> +
> +    return rc;
> +
> + fail:
> +    arch_vcpu_destroy(v);
> +    return rc;
> +}
> +
> +void arch_vcpu_destroy(struct vcpu *v)
> +{
> +    vfree((char *)v->arch.cpu_info + sizeof(struct cpu_info));
> +}

That doesn't look correct, you want to vfree what was allocated as the 
bottom of stack, i.e

v->arch.cpu_info + sizeof(struct cpu_info) - STACK_SIZE

Or alternatively introduce bottom of stack as a additional vcpu_arch field.

> diff --git a/xen/arch/riscv/include/asm/config.h b/xen/arch/riscv/include/asm/config.h
> index 1e08d3bf78be..86a95df018b5 100644
> --- a/xen/arch/riscv/include/asm/config.h
> +++ b/xen/arch/riscv/include/asm/config.h
> @@ -143,7 +143,8 @@
>   
>   #define SMP_CACHE_BYTES (1 << 6)
>   
> -#define STACK_SIZE PAGE_SIZE
> +#define STACK_ORDER 3
> +#define STACK_SIZE (PAGE_SIZE << STACK_ORDER)
>   
>   #define IDENT_AREA_SIZE 64
>   
> diff --git a/xen/arch/riscv/include/asm/current.h b/xen/arch/riscv/include/asm/current.h
> index 0c3ea70c2ec8..58c9f1506b7c 100644
> --- a/xen/arch/riscv/include/asm/current.h
> +++ b/xen/arch/riscv/include/asm/current.h
> @@ -21,6 +21,12 @@ struct pcpu_info {
>   /* tp points to one of these */
>   extern struct pcpu_info pcpu_info[NR_CPUS];
>   
> +/* Per-VCPU state that lives at the top of the stack */
> +struct cpu_info {
> +    /* This should be the first member. */
> +    struct cpu_user_regs guest_cpu_user_regs;
> +};
> +
>   #define set_processor_id(id)    do { \
>       tp->processor_id = (id);         \
>   } while (0)
> diff --git a/xen/arch/riscv/include/asm/domain.h b/xen/arch/riscv/include/asm/domain.h
> index 0d9b4c4b525e..ec7786c76199 100644
> --- a/xen/arch/riscv/include/asm/domain.h
> +++ b/xen/arch/riscv/include/asm/domain.h
> @@ -49,6 +49,8 @@ struct arch_vcpu
>           register_t ra;
>       } xen_saved_context;
>   
> +    struct cpu_info *cpu_info;
> +
>       /* CSRs */
>       register_t hedeleg;
>       register_t hideleg;
> diff --git a/xen/arch/riscv/stubs.c b/xen/arch/riscv/stubs.c
> index 29bdb65afbdf..9e30a9a3b50b 100644
> --- a/xen/arch/riscv/stubs.c
> +++ b/xen/arch/riscv/stubs.c
> @@ -121,16 +121,6 @@ void dump_pageframe_info(struct domain *d)
>       BUG_ON("unimplemented");
>   }
>   
> -int arch_vcpu_create(struct vcpu *v)
> -{
> -    BUG_ON("unimplemented");
> -}
> -
> -void arch_vcpu_destroy(struct vcpu *v)
> -{
> -    BUG_ON("unimplemented");
> -}
> -
>   void vcpu_switch_to_aarch64_mode(struct vcpu *v)
>   {
>       BUG_ON("unimplemented");



--
Teddy Astie | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech

Re: [PATCH v2 02/16] xen/riscv: implement arch_vcpu_{create,destroy}()

Posted by Oleksii Kurochko 2 weeks ago

Hello Teddy,

On 1/23/26 12:30 PM, Teddy Astie wrote:
> Hello,
>
> Le 22/01/2026 à 17:49, Oleksii Kurochko a écrit :
>> Introduce architecture-specific functions to create and destroy VCPUs.
>> Note that arch_vcpu_create() currently returns -EOPNOTSUPP, as the virtual
>> timer and interrupt controller are not yet implemented.
>>
>> As part of this change, add continue_new_vcpu(), which will be used after
>> the first context_switch() of a new vCPU. Since this functionality is not
>> yet implemented, continue_new_vcpu() is currently provided as a stub.
>>
>> Update the STACK_SIZE definition and introduce STACK_ORDER (to align with
>> other architectures) for allocating the vCPU stack.
>>
>> Introduce struct cpu_info to store per-vCPU state that lives at the top
>> of the vCPU's stack.
>>
>> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
>> ---
>> Changes in v2:
>>    - Drop BUILD_BUG_ON() in arch_vcpu_create() as a check isn't very useful.
>>    - Use vzalloc() instead of alloc_xenheap_page() to use the larger domheap to
>>      allocate vCPU's stack.
>>    - Drop printk() inside arch_vcpu_create() to not have potential big noise
>>      in console as it could be that an amount of vCPUs is pretty big.
>>    - Use XVFREE() instead of free_xenheap_pages() as vCPU's stack allocation
>>      happens with a usage of vzalloc() now.
>>    - Drop stack field as it is enough to have only cpu_info as stack pointer
>>      could be calculated based on cpu_info.
>>    - Drop cast when v.arch.cpu_info is inialized as it is not necessary
>>           to have it.
>>    - Drop memset() for arch.cpu_info() as it is enough to have vzalloc().
>> ---
>>    xen/arch/riscv/Makefile              |  1 +
>>    xen/arch/riscv/domain.c              | 59 ++++++++++++++++++++++++++++
>>    xen/arch/riscv/include/asm/config.h  |  3 +-
>>    xen/arch/riscv/include/asm/current.h |  6 +++
>>    xen/arch/riscv/include/asm/domain.h  |  2 +
>>    xen/arch/riscv/stubs.c               | 10 -----
>>    6 files changed, 70 insertions(+), 11 deletions(-)
>>    create mode 100644 xen/arch/riscv/domain.c
>>
>> diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
>> index 87c1148b0010..8863d4b15605 100644
>> --- a/xen/arch/riscv/Makefile
>> +++ b/xen/arch/riscv/Makefile
>> @@ -1,5 +1,6 @@
>>    obj-y += aplic.o
>>    obj-y += cpufeature.o
>> +obj-y += domain.o
>>    obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
>>    obj-y += entry.o
>>    obj-y += imsic.o
>> diff --git a/xen/arch/riscv/domain.c b/xen/arch/riscv/domain.c
>> new file mode 100644
>> index 000000000000..9c546267881b
>> --- /dev/null
>> +++ b/xen/arch/riscv/domain.c
>> @@ -0,0 +1,59 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +
>> +#include <xen/init.h>
>> +#include <xen/mm.h>
>> +#include <xen/sched.h>
>> +#include <xen/vmap.h>
>> +
>> +static void continue_new_vcpu(struct vcpu *prev)
>> +{
>> +    BUG_ON("unimplemented\n");
>> +}
>> +
>> +static void __init __maybe_unused build_assertions(void)
>> +{
>> +    /*
>> +     * Enforce the requirement documented in struct cpu_info that
>> +     * guest_cpu_user_regs must be the first field.
>> +     */
>> +    BUILD_BUG_ON(offsetof(struct cpu_info, guest_cpu_user_regs) != 0);
>> +}
>> +
>> +int arch_vcpu_create(struct vcpu *v)
>> +{
>> +    int rc = 0;
>> +    void *stack = vzalloc(STACK_SIZE);
>> +
> Are there alignment constraints for the stack ?

vzalloc() allocates page-aligned memory as far as I can see:
   ...
   va = __vmap(mfn, 1, pages, 1, PAGE_HYPERVISOR, type);
   ...
   
   where 1 -> means align and what will lead that in vm_alloc():
      ...
      start =(start +align)&~(align -1); ...

>
>> +    if ( !stack )
>> +        return -ENOMEM;
>> +
>> +    v->arch.cpu_info = stack + STACK_SIZE - sizeof(struct cpu_info);
>> +    memset(v->arch.cpu_info, 0, sizeof(*v->arch.cpu_info));
>> +
> Given that vzalloc ensures that the memory is cleared, you don't need to
> clear it another time.

Oh, right, missed to drop memset.

>
>> +    v->arch.xen_saved_context.sp = (register_t)v->arch.cpu_info;
>> +    v->arch.xen_saved_context.ra = (register_t)continue_new_vcpu;
>> +
> You probably also want to set the first parameter of continue_new_vcpu
> (struct vcpu *prev), or otherwise I don't think we want the "prev"
> parameter in continue_new_vcpu if it's always going to be 0.

It will be set by RISC-V ABI (prev will be stored in a0) when __context_switch()
will be called in context_switch():
   void context_switch(struct vcpu *prev, struct vcpu *next)
   {
     ASSERT(local_irq_is_enabled());
     ASSERT(prev != next);
     ASSERT(!vcpu_cpu_dirty(next));

     local_irq_disable();

     set_current(next);

     prev = __context_switch(prev, next);

     schedule_tail(prev);
   }
First call of the __context_switch() will lead to jump to continue_new_vcpu()
function which will have a0=prev.

>
> IIRC continue_new_vcpu is only meant to bootstrap the new vCPU, not just
> perform a context switch to it.
>
>> +    /* Idle VCPUs don't need the rest of this setup */
>> +    if ( is_idle_vcpu(v) )
>> +        return rc;
>> +
>> +    /*
>> +     * As the vtimer and interrupt controller (IC) are not yet implemented,
>> +     * return an error.
>> +     *
>> +     * TODO: Drop this once the vtimer and IC are implemented.
>> +     */
>> +    rc = -EOPNOTSUPP;
>> +    goto fail;
>> +
>> +    return rc;
>> +
>> + fail:
>> +    arch_vcpu_destroy(v);
>> +    return rc;
>> +}
>> +
>> +void arch_vcpu_destroy(struct vcpu *v)
>> +{
>> +    vfree((char *)v->arch.cpu_info + sizeof(struct cpu_info));
>> +}
> That doesn't look correct, you want to vfree what was allocated as the
> bottom of stack, i.e
>
> v->arch.cpu_info + sizeof(struct cpu_info) - STACK_SIZE

Agree formula should be correct, now it points to the end of the stack
memory.

>
> Or alternatively introduce bottom of stack as a additional vcpu_arch field.

There is not too much sense to have the separate field for that.

Thanks.

~ Oleksii

Re: [PATCH v2 02/16] xen/riscv: implement arch_vcpu_{create,destroy}()

Posted by Jan Beulich 2 weeks ago

On 26.01.2026 10:00, Oleksii Kurochko wrote:
> On 1/23/26 12:30 PM, Teddy Astie wrote:
>> Le 22/01/2026 à 17:49, Oleksii Kurochko a écrit :
>>> +    v->arch.xen_saved_context.sp = (register_t)v->arch.cpu_info;
>>> +    v->arch.xen_saved_context.ra = (register_t)continue_new_vcpu;
>>> +
>> You probably also want to set the first parameter of continue_new_vcpu
>> (struct vcpu *prev), or otherwise I don't think we want the "prev"
>> parameter in continue_new_vcpu if it's always going to be 0.
> 
> It will be set by RISC-V ABI (prev will be stored in a0) when __context_switch()
> will be called in context_switch():
>    void context_switch(struct vcpu *prev, struct vcpu *next)
>    {
>      ASSERT(local_irq_is_enabled());
>      ASSERT(prev != next);
>      ASSERT(!vcpu_cpu_dirty(next));
> 
>      local_irq_disable();
> 
>      set_current(next);
> 
>      prev = __context_switch(prev, next);
> 
>      schedule_tail(prev);
>    }
> First call of the __context_switch() will lead to jump to continue_new_vcpu()
> function which will have a0=prev.

Problem being that none of this code exists yet, and hence it's rather hard to
see how things will eventually fit together.

Jan

Re: [PATCH v2 02/16] xen/riscv: implement arch_vcpu_{create,destroy}()

Posted by Oleksii Kurochko 2 weeks ago

On 1/26/26 12:47 PM, Jan Beulich wrote:
> On 26.01.2026 10:00, Oleksii Kurochko wrote:
>> On 1/23/26 12:30 PM, Teddy Astie wrote:
>>> Le 22/01/2026 à 17:49, Oleksii Kurochko a écrit :
>>>> +    v->arch.xen_saved_context.sp = (register_t)v->arch.cpu_info;
>>>> +    v->arch.xen_saved_context.ra = (register_t)continue_new_vcpu;
>>>> +
>>> You probably also want to set the first parameter of continue_new_vcpu
>>> (struct vcpu *prev), or otherwise I don't think we want the "prev"
>>> parameter in continue_new_vcpu if it's always going to be 0.
>> It will be set by RISC-V ABI (prev will be stored in a0) when __context_switch()
>> will be called in context_switch():
>>     void context_switch(struct vcpu *prev, struct vcpu *next)
>>     {
>>       ASSERT(local_irq_is_enabled());
>>       ASSERT(prev != next);
>>       ASSERT(!vcpu_cpu_dirty(next));
>>
>>       local_irq_disable();
>>
>>       set_current(next);
>>
>>       prev = __context_switch(prev, next);
>>
>>       schedule_tail(prev);
>>     }
>> First call of the __context_switch() will lead to jump to continue_new_vcpu()
>> function which will have a0=prev.
> Problem being that none of this code exists yet, and hence it's rather hard to
> see how things will eventually fit together.

I am trying to avoid a large patch series, and this needs to be introduced
before we can implement context_switch(). At the moment, I'm trying to introduce
everything that I need for dom0less domain creation and context_switch() isn't
really needed at this stage and continue_to_new_vcpu() isn't really needed to be
implemented at this stage as well as context_switch().

The best I can do at the moment is either to write a better commit message
explaining how this will be used, or, specifically for continue_new_vcpu(), to
avoid introducing it for now and not initialise the ra register until the
remaining pieces are ready. But considering that I've already done in this way
then better commit message(s) should work.

~ Oleksii