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 <[email protected]>
Message-Id: <20200930041659[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 5a62fa4ee493e9b92a0e4661b3467ee6aa8d501c..35223eb63242835b7e02be93c20278e14cca82f3 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -145,8 +145,6 @@ 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))
@@ -170,6 +168,9 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
        kvm_pmu_refresh(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);
        kvm_x86_ops.update_exception_bitmap(vcpu);
 }