linux-kernel - [PATCH v9 04/19] KVM: selftests: Expose function to allocate guest vCPU stack

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Message-ID: <20250821042915.3712925-5-sagis@google.com>
Date: Wed, 20 Aug 2025 21:28:57 -0700
From: Sagi Shahar <sagis@...gle.com>
To: linux-kselftest@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, Sean Christopherson <seanjc@...gle.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Ryan Afranji <afranji@...gle.com>, 
	Andrew Jones <ajones@...tanamicro.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Erdem Aktas <erdemaktas@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Sagi Shahar <sagis@...gle.com>, Roger Wang <runanwang@...gle.com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	"Pratik R. Sampat" <pratikrajesh.sampat@....com>, Reinette Chatre <reinette.chatre@...el.com>, 
	Ira Weiny <ira.weiny@...el.com>, Chao Gao <chao.gao@...el.com>, 
	Chenyi Qiang <chenyi.qiang@...el.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH v9 04/19] KVM: selftests: Expose function to allocate guest
 vCPU stack

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@...gle.com>
---
 .../selftests/kvm/include/x86/processor.h       |  2 ++
 tools/testing/selftests/kvm/lib/x86/processor.c | 17 ++++++++++++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 5c16507f9b2d..8fcc5118683e 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -1111,6 +1111,8 @@ 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 b2a4b11ac8c0..1eae92957456 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -687,12 +687,9 @@ 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,
@@ -713,6 +710,15 @@ 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);
@@ -721,7 +727,8 @@ 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;
+	if (vm->type != KVM_X86_TDX_VM)
+		regs.rsp = kvm_allocate_vcpu_stack(vm);
 	vcpu_regs_set(vcpu, &regs);
 
 	/* Setup the MP state */
-- 
2.51.0.rc1.193.gad69d77794-goog