KVM: nSVM: Set exit_code_hi to -1 when synthesizing SVM_EXIT_ERR (failed VMRUN)

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
Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251113225621.1688428-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index da6e80b3ac353c4b433278c1ab1bc4470786e1a9..143a0ef02b03ed972015dcce20762d22c322463b 100644 (file)
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -983,7 +983,7 @@ 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;
@@ -1016,7 +1016,7 @@ out_exit_err:
        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;