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KVM: selftests: Adjust VM's initial stack address to align with SysV ABI spec

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Align the guest 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), NOT %rsp,
to be a multiple of 16 when control is transferred to the function
entry point. I.e. in a normal function call, %rsp needs to be 16-byte
aligned _before_ CALL, not after.

This fixes unexpected #GPs in guest code when the compiler uses SSE
instructions, e.g. to initialize memory, as many SSE instructions
require memory operands (including those on the stack) to be
16-byte-aligned.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Link: https://lore.kernel.org/r/20230227180601.104318-1-ackerleytng@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Ackerley Tng 2023-02-27 18:06:01 +00:00 • committed by Sean Christopherson
parent 5b1abc285a
commit 8264e85560
1 changed files with 17 additions and 1 deletions
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18
tools/testing/selftests/kvm/lib/x86_64/processor.c
View file

@ -5,6 +5,7 @@
* Copyright (C) 2018, Google LLC.
*/
#include "linux/bitmap.h"
#include "test_util.h"
#include "kvm_util.h"
#include "processor.h"
@ -573,6 +574,21 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id,
DEFAULT_GUEST_STACK_VADDR_MIN,
MEM_REGION_DATA);
stack_vaddr += 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_vaddr, PAGE_SIZE),
"__vm_vaddr_alloc() did not provide a page-aligned address");
stack_vaddr -= 8;
vcpu = __vm_vcpu_add(vm, vcpu_id);
vcpu_init_cpuid(vcpu, kvm_get_supported_cpuid());
vcpu_setup(vm, vcpu);
@ -580,7 +596,7 @@ 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 + (DEFAULT_STACK_PGS * getpagesize());
regs.rsp = stack_vaddr;
regs.rip = (unsigned long) guest_code;
vcpu_regs_set(vcpu, &regs);