linux-kernel - [PATCH 2/5] KVM: x86: Invoke vendor's vcpu_after_set

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Message-Id: <20200930041659.28181-3-sean.j.christopherson@intel.com>
Date:   Tue, 29 Sep 2020 21:16:56 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>
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 <sean.j.christopherson@...el.com>
---
 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)
 	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);
 }

-- 
2.28.0