linux-kernel - [PATCH 06/26] KVM: x86: Move MSR_IA32_BNDCFGS existence checks into vendor code

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Date:   Wed, 29 Jan 2020 15:46:20 -0800
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
Subject: [PATCH 06/26] KVM: x86: Move MSR_IA32_BNDCFGS existence checks into vendor code

Move the MSR_IA32_BNDCFGS existence check into vendor code by way of
->has_virtualized_msr().  AMD does not support MPX, and given that Intel
is in the process of removing MPX, it's extremely unlikely AMD will ever
support MPX.

Note, invoking ->has_virtualized_msr() requires an extra retpoline, but
kvm_init_msr_list() is not a hot path.  As alluded to above, the
motivation is to quarantine MPX as much as possible.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/svm.c     | 2 ++
 arch/x86/kvm/vmx/vmx.c | 2 ++
 arch/x86/kvm/x86.c     | 4 ----
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 4c8427f57b71..504118c49f46 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5990,6 +5990,8 @@ static bool svm_has_virtualized_msr(u32 index)
 	switch (index) {
 	case MSR_TSC_AUX:
 		return boot_cpu_has(X86_FEATURE_RDTSCP);
+	case MSR_IA32_BNDCFGS:
+		return false;
 	default:
 		break;
 	}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9588914e941e..dbeef64f7409 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6279,6 +6279,8 @@ static bool vmx_has_virtualized_msr(u32 index)
 	switch (index) {
 	case MSR_TSC_AUX:
 		return cpu_has_vmx_rdtscp();
+	case MSR_IA32_BNDCFGS:
+		return kvm_mpx_supported();
 	default:
 		break;
 	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a8619c52ea86..70cbb9164088 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5237,10 +5237,6 @@ static void kvm_init_msr_list(void)
 		 * to the guests in some cases.
 		 */
 		switch (msr_index) {
-		case MSR_IA32_BNDCFGS:
-			if (!kvm_mpx_supported())
-				continue;
-			break;
 		case MSR_IA32_RTIT_CTL:
 		case MSR_IA32_RTIT_STATUS:
 			if (!kvm_x86_ops->pt_supported())
-- 
2.24.1