On Thu, Nov 13, 2025 at 02:56:14PM -0800, Sean Christopherson wrote:
> Set exit_code_hi to -1u as a temporary band-aid to fix a long-standing
> (effectively since KVM's inception) bug where KVM treats the exit code as
> a 32-bit value, when in reality it's a 64-bit value. Per the APM, offset
> 0x70 is a single 64-bit value:
>
> 070h 63:0 EXITCODE
>
> And a sane reading of the error values defined in "Table C-1. SVM Intercept
> Codes" is that negative values use the full 64 bits:
>
> –1 VMEXIT_INVALID Invalid guest state in VMCB.
> –2 VMEXIT_BUSYBUSY bit was set in the VMSA
> –3 VMEXIT_IDLE_REQUIREDThe sibling thread is not in an idle state
> -4 VMEXIT_INVALID_PMC Invalid PMC state
>
> And that interpretation is confirmed by testing on Milan and Turin (by
> setting bits in CR0[63:32] to generate VMEXIT_INVALID on VMRUN).
>
> Furthermore, Xen has treated exitcode as a 64-bit value since HVM support
> was adding in 2006 (see Xen commit d1bd157fbc ("Big merge the HVM
> full-virtualisation abstractions.")).
>
> Cc: Jim Mattson <jmattson@google.com>
> Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
> ---
> arch/x86/kvm/svm/nested.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index c81005b24522..ba0f11c68372 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -985,7 +985,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> if (!nested_vmcb_check_save(vcpu) ||
> !nested_vmcb_check_controls(vcpu)) {
> vmcb12->control.exit_code = SVM_EXIT_ERR;
> - vmcb12->control.exit_code_hi = 0;
> + vmcb12->control.exit_code_hi = -1u;
> vmcb12->control.exit_info_1 = 0;
> vmcb12->control.exit_info_2 = 0;
> goto out;
> @@ -1018,7 +1018,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> svm->soft_int_injected = false;
>
> svm->vmcb->control.exit_code = SVM_EXIT_ERR;
> - svm->vmcb->control.exit_code_hi = 0;
> + svm->vmcb->control.exit_code_hi = -1u;
> svm->vmcb->control.exit_info_1 = 0;
> svm->vmcb->control.exit_info_2 = 0;
>
> --
> 2.52.0.rc1.455.g30608eb744-goog
>