linux-kernel - [PATCH 2/3] KVM: nVMX: fix wrong condition for SPEC_CTRL and PRED

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Date:   Wed, 21 Feb 2018 22:41:36 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     x86@...nel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org
Subject: [PATCH 2/3] KVM: nVMX: fix wrong condition for SPEC_CTRL and PRED_CMD MSRs

We need to change the default all-1s bitmap if the MSRs are _not_
intercepted.  However, the code was disabling the intercept when it was
_enabled_ in the VMCS01.  This is not causing bigger trouble,
because vmx_vcpu_run checks the VMCS02's MSR bitmap and would do the
right thing even if fed garbage... but it's obviously a bug and it can
cause extra MSR reads and writes when running nested guests.

Fixes: d28b387fb74da95d69d2615732f50cceb38e9a4d
Fixes: 15d45071523d89b3fb7372e2135fbd72f6af9506
Cc: x86@...nel.org
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: KarimAllah Ahmed <karahmed@...zon.de>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Jim Mattson <jmattson@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5caeb8dc5bda..af89d377681d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10235,7 +10235,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 		return false;
 
 	if (!nested_cpu_has_virt_x2apic_mode(vmcs12) &&
-	    !pred_cmd && !spec_ctrl)
+	    pred_cmd && spec_ctrl)
 		return false;
 
 	page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->msr_bitmap);
@@ -10278,13 +10278,13 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 			MSR_TYPE_W);
 	}
 
-	if (spec_ctrl)
+	if (!spec_ctrl)
 		nested_vmx_disable_intercept_for_msr(
 					msr_bitmap_l1, msr_bitmap_l0,
 					MSR_IA32_SPEC_CTRL,
 					MSR_TYPE_R | MSR_TYPE_W);
 
-	if (pred_cmd)
+	if (!pred_cmd)
 		nested_vmx_disable_intercept_for_msr(
 					msr_bitmap_l1, msr_bitmap_l0,
 					MSR_IA32_PRED_CMD,
-- 
1.8.3.1