Re: [PATCH v15 14/23] KVM: selftests: Expose function to allocate vCPU stack

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

On 10/9/2026 3:56 PM, Xiaoyao Li wrote:
> On 10/2/2026 3:37 AM, Lisa Wang wrote:
>> From: Sagi Shahar <sagis@google.com>
>>
>> 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@google.com>
>> Signed-off-by: Lisa Wang <wyihan@google.com>
>> Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
>> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>>  .../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, &regs);
>>  }
>>  
>> -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@smtp.kernel.org/
> 
>>  {
>>  	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, &regs);
>> -	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, &regs);
>>  
>>  	/* Setup the MP state */
>>
>