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Subject[PATCH 2/5] KVM: x86: Invoke vendor's vcpu_after_set_cpuid() after all common updates
Move the call to kvm_x86_ops.vcpu_after_set_cpuid() to the very end of
kvm_vcpu_after_set_cpuid() to allow the vendor implementation to react
to changes made by the common code. In the near future, this will be
used by VMX to update its CR4 guest/host masks to account for reserved
bits. In the long term, SGX support will update the allowed XCR0 mask
for enclaves based on the vCPU's allowed XCR0.

vcpu_after_set_cpuid() (nee kvm_update_cpuid()) was originally added by
commit 2acf923e38fb ("KVM: VMX: Enable XSAVE/XRSTOR for guest"), and was
called separately after kvm_x86_ops.vcpu_after_set_cpuid() (nee
kvm_x86_ops->cpuid_update()). There is no indication that the placement
of the common code updates after the vendor updates was anything more
than a "new function at the end" decision.

Inspection of the current code reveals no dependency on kvm_x86_ops'
vcpu_after_set_cpuid() in kvm_vcpu_after_set_cpuid() or any of its
helpers. The bulk of the common code depends only on the guest's CPUID
configuration, kvm_mmu_reset_context() does not consume dynamic vendor
state, and there are no collisions between kvm_pmu_refresh() and VMX's
update of PT state.

Signed-off-by: Sean Christopherson <>
arch/x86/kvm/cpuid.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 37c3668a774f..963bad7bc0ff 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -121,8 +121,6 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
struct kvm_lapic *apic = vcpu->arch.apic;
struct kvm_cpuid_entry2 *best;

- kvm_x86_ops.vcpu_after_set_cpuid(vcpu);
best = kvm_find_cpuid_entry(vcpu, 1, 0);
if (best && apic) {
if (cpuid_entry_has(best, X86_FEATURE_TSC_DEADLINE_TIMER))
@@ -146,6 +144,9 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vcpu->arch.cr4_guest_rsvd_bits =
__cr4_reserved_bits(guest_cpuid_has, vcpu);
+ /* Invoke the vendor callback only after the above state is updated. */
+ kvm_x86_ops.vcpu_after_set_cpuid(vcpu);

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