Re: [PATCH v15 14/23] KVM: selftests: Expose function to allocate vCPU stack
From: Binbin Wu
Date: Fri Oct 09 2026 - 23:56:23 EST
On 10/9/2026 3:56 PM, Xiaoyao Li wrote:
> On 10/2/2026 3:37 AM, Lisa Wang wrote:
>> From: Sagi Shahar <sagis@xxxxxxxxxx>
>>
>> Introduce kvm_allocate_vcpu_stack() to allocate a vCPU's stack
>> in preparation for TDX to allocate a vCPU's stack and initialize
>> its stack pointer.
>>
>> TDX VMs' registers are protected state and cannot be initialized
>> using the KVM_SET_REGS ioctl() that is used for normal VMs. A TDX
>> vCPU's stack address will be a property of the TDX specific boot code
>> that initializes the vCPUs' stack pointers at boot.
>>
>> Signed-off-by: Sagi Shahar <sagis@xxxxxxxxxx>
>> Signed-off-by: Lisa Wang <wyihan@xxxxxxxxxx>
>> Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
>> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>> Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
>> ---
>> .../testing/selftests/kvm/include/x86/processor.h | 2 ++
>> tools/testing/selftests/kvm/lib/x86/processor.c | 25 +++++++++++++++++++---
>> 2 files changed, 24 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
>> index 8854ee052d29..1eb380dd216c 100644
>> --- a/tools/testing/selftests/kvm/include/x86/processor.h
>> +++ b/tools/testing/selftests/kvm/include/x86/processor.h
>> @@ -1212,6 +1212,8 @@ static inline void vcpu_clear_cpuid_feature(struct kvm_vcpu *vcpu,
>> vcpu_set_or_clear_cpuid_feature(vcpu, feature, false);
>> }
>>
>> +gva_t kvm_allocate_vcpu_stack(struct kvm_vm *vm);
>> +
>> u64 vcpu_get_msr(struct kvm_vcpu *vcpu, u64 msr_index);
>> int _vcpu_set_msr(struct kvm_vcpu *vcpu, u64 msr_index, u64 msr_value);
>>
>> diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
>> index da430d4e7765..4a753fb43007 100644
>> --- a/tools/testing/selftests/kvm/lib/x86/processor.c
>> +++ b/tools/testing/selftests/kvm/lib/x86/processor.c
>> @@ -851,12 +851,31 @@ void vcpu_arch_set_entry_point(struct kvm_vcpu *vcpu, void *guest_code)
>> vcpu_regs_set(vcpu, ®s);
>> }
>>
>> -struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, u32 vcpu_id)
>> +gva_t kvm_allocate_vcpu_stack(struct kvm_vm *vm)
>
> Besides what Sashiko pointed out[1], this patch was just messed up during the
> rebase and it even doesn't compile.
Yes.
And since the upstream code already has vm_alloc_stack(), which basically does
the same thing.
I think this patch can be dropped.
>
> [1] https://lore.kernel.org/all/20261002091331.BA23F1F00893@xxxxxxxxxxxxxxx/
>
>> {
>> struct kvm_mp_state mp_state;
>> struct kvm_regs regs;
>> + gva_t stack_gva;
>> struct kvm_vcpu *vcpu;
>>
>> + stack_gva = __vm_alloc(vm, DEFAULT_STACK_PGS * getpagesize(),
>> + DEFAULT_GUEST_STACK_VADDR_MIN, MEM_REGION_DATA);
>> +
>> + stack_gva += DEFAULT_STACK_PGS * getpagesize();
>> +
>> + /*
>> + * Align stack to match calling sequence requirements in section "The
>> + * Stack Frame" of the System V ABI AMD64 Architecture Processor
>> + * Supplement, which requires the value (%rsp + 8) to be a multiple of
>> + * 16 when control is transferred to the function entry point.
>> + *
>> + * If this code is ever used to launch a vCPU with 32-bit entry point it
>> + * may need to subtract 4 bytes instead of 8 bytes.
>> + */
>> + TEST_ASSERT(IS_ALIGNED(stack_gva, PAGE_SIZE),
>> + "__vm_alloc() did not provide a page-aligned address");
>> + stack_gva -= 8;
>> +
>> vcpu = __vm_vcpu_add(vm, vcpu_id);
>> vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());
>> vcpu_init_sregs(vm, vcpu);
>> @@ -864,8 +883,8 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, u32 vcpu_id)
>>
>> /* Setup guest general purpose registers */
>> vcpu_regs_get(vcpu, ®s);
>> - regs.rflags = regs.rflags | X86_EFLAGS_FIXED;
>> - regs.rsp = vm_alloc_stack(vm, DEFAULT_STACK_PGS);
>> + regs.rflags = regs.rflags | 0x2;
>> + regs.rsp = kvm_allocate_vcpu_stack(vm);
>> vcpu_regs_set(vcpu, ®s);
>>
>> /* Setup the MP state */
>>
>