Re: [PATCH v10 03/21] KVM: selftests: Expose function to allocate guest vCPU stack

[Binbin Wu <binbin.wu@linux.intel.com>]

On 9/4/2025 2:54 PM, Sagi Shahar wrote:
> TDX guests' registers cannot be initialized directly using
> vcpu_regs_set(), hence the stack pointer needs to be initialized by
> the guest itself, running boot code beginning at the reset vector.
>
> Expose the function to allocate the guest stack so that TDX
> initialization code can allocate it itself and skip the allocation in
> vm_arch_vcpu_add() in that case.
>
> Signed-off-by: Sagi Shahar <sagis@google.com>

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>

> ---
>   .../selftests/kvm/include/x86/processor.h        |  2 ++
>   tools/testing/selftests/kvm/lib/x86/processor.c  | 16 +++++++++++-----
>   2 files changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
> index f610c09cadf4..8e75df5e6bc9 100644
> --- a/tools/testing/selftests/kvm/include/x86/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86/processor.h
> @@ -1109,6 +1109,8 @@ static inline void vcpu_clear_cpuid_feature(struct kvm_vcpu *vcpu,
>   	vcpu_set_or_clear_cpuid_feature(vcpu, feature, false);
>   }
>   
> +vm_vaddr_t kvm_allocate_vcpu_stack(struct kvm_vm *vm);
> +
>   uint64_t vcpu_get_msr(struct kvm_vcpu *vcpu, uint64_t msr_index);
>   int _vcpu_set_msr(struct kvm_vcpu *vcpu, uint64_t msr_index, uint64_t msr_value);
>   
> diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
> index 83efcf48faad..82369373e843 100644
> --- a/tools/testing/selftests/kvm/lib/x86/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86/processor.c
> @@ -658,12 +658,9 @@ void vcpu_arch_set_entry_point(struct kvm_vcpu *vcpu, void *guest_code)
>   	vcpu_regs_set(vcpu, &regs);
>   }
>   
> -struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
> +vm_vaddr_t kvm_allocate_vcpu_stack(struct kvm_vm *vm)
>   {
> -	struct kvm_mp_state mp_state;
> -	struct kvm_regs regs;
>   	vm_vaddr_t stack_vaddr;
> -	struct kvm_vcpu *vcpu;
>   
>   	stack_vaddr = __vm_vaddr_alloc(vm, DEFAULT_STACK_PGS * getpagesize(),
>   				       DEFAULT_GUEST_STACK_VADDR_MIN,
> @@ -684,6 +681,15 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
>   		    "__vm_vaddr_alloc() did not provide a page-aligned address");
>   	stack_vaddr -= 8;
>   
> +	return stack_vaddr;
> +}
> +
> +struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
> +{
> +	struct kvm_mp_state mp_state;
> +	struct kvm_regs regs;
> +	struct kvm_vcpu *vcpu;
> +
>   	vcpu = __vm_vcpu_add(vm, vcpu_id);
>   	vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());
>   	vcpu_init_sregs(vm, vcpu);
> @@ -692,7 +698,7 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
>   	/* Setup guest general purpose registers */
>   	vcpu_regs_get(vcpu, &regs);
>   	regs.rflags = regs.rflags | 0x2;
> -	regs.rsp = stack_vaddr;
> +	regs.rsp = kvm_allocate_vcpu_stack(vm);
>   	vcpu_regs_set(vcpu, &regs);
>   
>   	/* Setup the MP state */