[PATCH v5 10/13] KVM: selftests: Refactor allocating guest stack into a helper

Yosry Ahmed
2026-04-30T20:28:05Z

In preparation for reusing the logic to allocate stacks for nested
guests, refactoring allocating a guest stack and aligning RSP into a
helper.

No functional change intended.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
.../testing/selftests/kvm/lib/x86/processor.c | 45 ++++++++++---------
1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index b51467d70f6e7..94a1cadb2b26b 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -778,6 +778,30 @@ void assert_on_unhandled_exception(struct kvm_vcpu *vcpu)
REPORT_GUEST_ASSERT(uc);
}

+static gva_t vm_alloc_stack(struct kvm_vm *vm, int nr_pages)
+{
+ int size = nr_pages * getpagesize();
+ gva_t stack_gva;
+
+ stack_gva = __vm_alloc(vm, size, DEFAULT_GUEST_STACK_VADDR_MIN, MEM_REGION_DATA);
+ stack_gva += size;
+
+ /*
+ * 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;
+
+ return stack_gva;
+}
+
void kvm_arch_vm_post_create(struct kvm_vm *vm, unsigned int nr_vcpus)
{
int r;
@@ -820,27 +844,8 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, u32 vcpu_id)
{
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);
@@ -849,7 +854,7 @@ 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 | 0x2;
- regs.rsp = stack_gva;
+ regs.rsp = vm_alloc_stack(vm, DEFAULT_STACK_PGS);
vcpu_regs_set(vcpu, &regs);

/* Setup the MP state */
--
2.54.0.545.g6539524ca2-goog