From: Ackerley Tng <ackerleytng@google.com>

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.

Store the stack address as part of struct kvm_vcpu so that it can
be accessible later to be passed to the boot code for rsp
initialization.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Sagi Shahar <sagis@google.com>
---
 tools/testing/selftests/kvm/include/kvm_util.h  | 1 +
 tools/testing/selftests/kvm/lib/x86/processor.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 9994861d2acb..5c4ca25803ac 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -58,6 +58,7 @@ struct kvm_vcpu {
 	int fd;
 	struct kvm_vm *vm;
 	struct kvm_run *run;
+	vm_vaddr_t initial_stack_addr;
 #ifdef __x86_64__
 	struct kvm_cpuid2 *cpuid;
 #endif
diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index 002303e2a572..da6e9315ebe2 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -694,6 +694,8 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
 	vcpu_init_sregs(vm, vcpu);
 	vcpu_init_xcrs(vm, vcpu);
 
+	vcpu->initial_stack_addr = stack_vaddr;
+
 	/* Setup guest general purpose registers */
 	vcpu_regs_get(vcpu, &regs);
 	regs.rflags = regs.rflags | 0x2;
-- 
2.51.0.rc0.155.g4a0f42376b-goog

On Thu, Aug 07, 2025, Sagi Shahar wrote:
> From: Ackerley Tng <ackerleytng@google.com>
> 
> 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.
> 
> Store the stack address as part of struct kvm_vcpu so that it can
> be accessible later to be passed to the boot code for rsp
> initialization.

NAK.  This bleeds x86 details into common code, and is again a convoluted way of
passing information into TDX specific code.

> 
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Sagi Shahar <sagis@google.com>
> ---
>  tools/testing/selftests/kvm/include/kvm_util.h  | 1 +
>  tools/testing/selftests/kvm/lib/x86/processor.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 9994861d2acb..5c4ca25803ac 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -58,6 +58,7 @@ struct kvm_vcpu {
>  	int fd;
>  	struct kvm_vm *vm;
>  	struct kvm_run *run;
> +	vm_vaddr_t initial_stack_addr;
>  #ifdef __x86_64__
>  	struct kvm_cpuid2 *cpuid;
>  #endif
> diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
> index 002303e2a572..da6e9315ebe2 100644
> --- a/tools/testing/selftests/kvm/lib/x86/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86/processor.c
> @@ -694,6 +694,8 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id)
>  	vcpu_init_sregs(vm, vcpu);
>  	vcpu_init_xcrs(vm, vcpu);
>  
> +	vcpu->initial_stack_addr = stack_vaddr;
> +
>  	/* Setup guest general purpose registers */
>  	vcpu_regs_get(vcpu, &regs);
>  	regs.rflags = regs.rflags | 0x2;
> -- 
> 2.51.0.rc0.155.g4a0f42376b-goog
>