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

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