linux-kernel - [PATCH 5.0 116/117] KVM: x86: nVMX: fix x2APIC VTPR read intercept

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Message-Id: <20190415183750.654071873@linuxfoundation.org>
Date:   Mon, 15 Apr 2019 21:01:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marc Orr <marcorr@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.0 116/117] KVM: x86: nVMX: fix x2APIC VTPR read intercept

From: Marc Orr <marcorr@...gle.com>

commit c73f4c998e1fd4249b9edfa39e23f4fda2b9b041 upstream.

Referring to the "VIRTUALIZING MSR-BASED APIC ACCESSES" chapter of the
SDM, when "virtualize x2APIC mode" is 1 and "APIC-register
virtualization" is 0, a RDMSR of 808H should return the VTPR from the
virtual APIC page.

However, for nested, KVM currently fails to disable the read intercept
for this MSR. This means that a RDMSR exit takes precedence over
"virtualize x2APIC mode", and KVM passes through L1's TPR to L2,
instead of sourcing the value from L2's virtual APIC page.

This patch fixes the issue by disabling the read intercept, in VMCS02,
for the VTPR when "APIC-register virtualization" is 0.

The issue described above and fix prescribed here, were verified with
a related patch in kvm-unit-tests titled "Test VMX's virtualize x2APIC
mode w/ nested".

Signed-off-by: Marc Orr <marcorr@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Fixes: c992384bde84f ("KVM: vmx: speed up MSR bitmap merge")
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/vmx/nested.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -578,7 +578,7 @@ static inline bool nested_vmx_prepare_ms
 		nested_vmx_disable_intercept_for_msr(
 			msr_bitmap_l1, msr_bitmap_l0,
 			X2APIC_MSR(APIC_TASKPRI),
-			MSR_TYPE_W);
+			MSR_TYPE_R | MSR_TYPE_W);

 		if (nested_cpu_has_vid(vmcs12)) {
 			nested_vmx_disable_intercept_for_msr(