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KVM: selftests: Fix RAX and RFLAGS VMCB offsets when running L2

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The offsets used (0x170 and 0x1f8) are offsets within vmcb_save_area,
not vmcb. The correct offsets should include the base of vmcb_save_area
within vmcb (which is 0x400 -- so 0x570 and 0x5f8).

Instead of just correcting the offsets, use vmcb->save.rax and
vmcb->save.rflags as parameters to the asm block and avoid hardcoding
offsets completely. While at it, also use guest_regs.rax directly
instead of assuming it's at offset 0 of guest_regs.

Note: "+m" must be used for vmcb_rax and vmcb_rflags, as caching those
fields in registers would be wrong as the underlying KVM will update
them in memory.

The same problem was recently fixed (differently) for kvm-unit-tests
[1].

[1]https://lore.kernel.org/all/20260521092311.86030-1-pbonzini@redhat.com/

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260518202514.2037078-1-yosry%40kernel.org?part=1
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260728174232.2423257-3-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Yosry Ahmed
2026-07-28 17:42:21 +00:00
committed by Sean Christopherson
parent 9be54a8265
commit 53f4ad49d7
1 changed files with 11 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
tools/testing/selftests/kvm/lib/x86/svm.c
View File

@@ -164,19 +164,22 @@ void run_guest(struct vmcb *vmcb, u64 vmcb_gpa)
{
asm volatile (
"vmload %[vmcb_gpa]\n\t"
"mov rflags, %%r15\n\t" // rflags
"mov %%r15, 0x170(%[vmcb])\n\t"
"mov guest_regs, %%r15\n\t" // rax
"mov %%r15, 0x1f8(%[vmcb])\n\t"
"mov rflags, %%r15\n\t"
"mov %%r15, %[vmcb_rflags]\n\t"
"mov %[guest_regs_rax], %%r15\n\t"
"mov %%r15, %[vmcb_rax]\n\t"
LOAD_GPR_C
"vmrun %[vmcb_gpa]\n\t"
SAVE_GPR_C
"mov 0x170(%[vmcb]), %%r15\n\t" // rflags
"mov %[vmcb_rflags], %%r15\n\t"
"mov %%r15, rflags\n\t"
"mov 0x1f8(%[vmcb]), %%r15\n\t" // rax
"mov %%r15, guest_regs\n\t"
"mov %[vmcb_rax], %%r15\n\t" // rax
"mov %%r15, %[guest_regs_rax]\n\t"
"vmsave %[vmcb_gpa]\n\t"
: : [vmcb] "r" (vmcb), [vmcb_gpa] "a" (vmcb_gpa)
: [vmcb_rflags] "+m" (vmcb->save.rflags),
[vmcb_rax] "+m" (vmcb->save.rax),
[guest_regs_rax] "+rm" (guest_regs.rax)
: [vmcb_gpa] "a" (vmcb_gpa)
: "r15", "memory");
}