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KVM: SVM: Refresh vcpu->arch.cr{0,3} prior to invoking fastpath handler

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Refresh KVM's copies of CR0 and CR3 from the VMCB prior to (potentially)
invoking a fastpath handler to ensure that KVM doesn't consume stale
state.  While it's unlikely KVM will ever consume CR3 or CR0.{TS,MP} in
the fastpath, grabbing the values from the VMCB is inexpensive, i.e. the
risk of subtle bugs far outweighs the reward of deferring reads for a
small subset of VM-Exits.

Note, KVM doesn't currently consume CR3 or CR0.{TS,MP} in the fastpath,
as KVM requires next_rip to be valid (i.e. KVM doesn't read CR3 to decode
the instruction), CR0.MP is never consumed, and CR0.TS is only consumed by
the full emulator.

Reviewed-by: Nikunj A. Dadhania <nikunj@amd.com>
Link: https://patch.msgid.link/20260423162628.490962-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-04-23 09:26:28 -07:00
parent 0ffedf4391
commit b21525756e
1 changed files with 6 additions and 8 deletions
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14
arch/x86/kvm/svm/svm.c
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@ -3663,14 +3663,6 @@ static int svm_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
struct vcpu_svm *svm = to_svm(vcpu);
struct kvm_run *kvm_run = vcpu->run;
/* SEV-ES guests must use the CR write traps to track CR registers. */
if (!is_sev_es_guest(vcpu)) {
if (!svm_is_intercept(svm, INTERCEPT_CR0_WRITE))
vcpu->arch.cr0 = svm->vmcb->save.cr0;
if (npt_enabled)
vcpu->arch.cr3 = svm->vmcb->save.cr3;
}
if (unlikely(exit_fastpath == EXIT_FASTPATH_EXIT_USERSPACE))
return 0;
@ -4527,11 +4519,17 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
x86_spec_ctrl_restore_host(svm->virt_spec_ctrl);
/* SEV-ES guests must use the CR write traps to track CR registers. */
if (!is_sev_es_guest(vcpu)) {
vcpu->arch.cr2 = svm->vmcb->save.cr2;
vcpu->arch.regs[VCPU_REGS_RAX] = svm->vmcb->save.rax;
vcpu->arch.regs[VCPU_REGS_RSP] = svm->vmcb->save.rsp;
vcpu->arch.rip = svm->vmcb->save.rip;
if (!svm_is_intercept(svm, INTERCEPT_CR0_WRITE))
vcpu->arch.cr0 = svm->vmcb->save.cr0;
if (npt_enabled)
vcpu->arch.cr3 = svm->vmcb->save.cr3;
}
kvm_reset_dirty_registers(vcpu);