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KVM: SVM: Add a helper to detect VMRUN failures

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Add a helper to detect VMRUN failures so that KVM can guard against its
own long-standing bug, where KVM neglects to set exitcode[63:32] when
synthesizing a nested VMFAIL_INVALID VM-Exit.  This will allow fixing
KVM's mess of treating exitcode as two separate 32-bit values without
breaking KVM-on-KVM when running on an older, unfixed KVM.

Cc: Jim Mattson <jmattson@google.com>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251230211347.4099600-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-12-30 13:13:40 -08:00
parent d23051f59a
commit 217463aa32
3 changed files with 14 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
arch/x86/kvm/svm/nested.c
View File

@ -1167,7 +1167,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
vmcb12->control.exit_info_1 = vmcb02->control.exit_info_1;
vmcb12->control.exit_info_2 = vmcb02->control.exit_info_2;
if (vmcb12->control.exit_code != SVM_EXIT_ERR)
if (!svm_is_vmrun_failure(vmcb12->control.exit_code))
nested_save_pending_event_to_vmcb12(svm, vmcb12);
if (guest_cpu_cap_has(vcpu, X86_FEATURE_NRIPS))
@ -1463,6 +1463,9 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
u32 exit_code = svm->vmcb->control.exit_code;
int vmexit = NESTED_EXIT_HOST;
if (svm_is_vmrun_failure(exit_code))
return NESTED_EXIT_DONE;
switch (exit_code) {
case SVM_EXIT_MSR:
vmexit = nested_svm_exit_handled_msr(svm);
@ -1470,7 +1473,7 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
case SVM_EXIT_IOIO:
vmexit = nested_svm_intercept_ioio(svm);
break;
case SVM_EXIT_EXCP_BASE ... SVM_EXIT_EXCP_BASE + 0x1f: {
case SVM_EXIT_EXCP_BASE ... SVM_EXIT_EXCP_BASE + 0x1f:
/*
* Host-intercepted exceptions have been checked already in
* nested_svm_exit_special. There is nothing to do here,
@ -1478,15 +1481,10 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
*/
vmexit = NESTED_EXIT_DONE;
break;
}
case SVM_EXIT_ERR: {
vmexit = NESTED_EXIT_DONE;
break;
}
default: {
default:
if (vmcb12_is_intercept(&svm->nested.ctl, exit_code))
vmexit = NESTED_EXIT_DONE;
}
break;
}
return vmexit;

4
arch/x86/kvm/svm/svm.c
View File

@ -3564,7 +3564,7 @@ static int svm_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
return 1;
}
if (svm->vmcb->control.exit_code == SVM_EXIT_ERR) {
if (svm_is_vmrun_failure(svm->vmcb->control.exit_code)) {
kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY;
kvm_run->fail_entry.hardware_entry_failure_reason
= svm->vmcb->control.exit_code;
@ -4346,7 +4346,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
/* Track VMRUNs that have made past consistency checking */
if (svm->nested.nested_run_pending &&
svm->vmcb->control.exit_code != SVM_EXIT_ERR)
!svm_is_vmrun_failure(svm->vmcb->control.exit_code))
++vcpu->stat.nested_run;
svm->nested.nested_run_pending = 0;

5
arch/x86/kvm/svm/svm.h
View File

@ -425,6 +425,11 @@ static __always_inline struct vcpu_svm *to_svm(struct kvm_vcpu *vcpu)
return container_of(vcpu, struct vcpu_svm, vcpu);
}
static inline bool svm_is_vmrun_failure(u64 exit_code)
{
return (u32)exit_code == (u32)SVM_EXIT_ERR;
}
/*
* Only the PDPTRs are loaded on demand into the shadow MMU. All other
* fields are synchronized on VM-Exit, because accessing the VMCB is cheap.