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

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 */