linux-kernel - [PATCH 2/2] KVM: x86: Don't update vcpu->arch.pv_eoi.msr_val when a bogus value was written to MSR_KVM_PV_EOI

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Message-Id: <20211108152819.12485-3-vkuznets@redhat.com>
Date:   Mon,  8 Nov 2021 16:28:19 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Li RongQing <lirongqing@...du.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] KVM: x86: Don't update vcpu->arch.pv_eoi.msr_val when a bogus value was written to MSR_KVM_PV_EOI_EN

When kvm_gfn_to_hva_cache_init() call from kvm_lapic_set_pv_eoi() fails,
MSR write to MSR_KVM_PV_EOI_EN results in #GP so it is reasonable to
expect that the value we keep internally in KVM wasn't updated.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/lapic.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 3573b50d9036..4388d22df500 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2857,20 +2857,25 @@ int kvm_lapic_set_pv_eoi(struct kvm_vcpu *vcpu, u64 data, unsigned long len)
 	u64 addr = data & ~KVM_MSR_ENABLED;
 	struct gfn_to_hva_cache *ghc = &vcpu->arch.pv_eoi.data;
 	unsigned long new_len;
+	int ret;
 
 	if (!IS_ALIGNED(addr, 4))
 		return 1;
 
-	vcpu->arch.pv_eoi.msr_val = data;
-	if (!pv_eoi_enabled(vcpu))
-		return 0;
+	if (data & KVM_MSR_ENABLED) {
+		if (addr == ghc->gpa && len <= ghc->len)
+			new_len = ghc->len;
+		else
+			new_len = len;
 
-	if (addr == ghc->gpa && len <= ghc->len)
-		new_len = ghc->len;
-	else
-		new_len = len;
+		ret = kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, addr, new_len);
+		if (ret)
+			return ret;
+	}
+
+	vcpu->arch.pv_eoi.msr_val = data;
 
-	return kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, addr, new_len);
+	return 0;
 }
 
 int kvm_apic_accept_events(struct kvm_vcpu *vcpu)
-- 
2.31.1