[PATCH 06/15] KVM: SVM: Disable intercepts for all direct access MSRs on MSR filter changes

[Aaron Lewis <aaronlewis@google.com>]

From: Anish Ghulati <aghulati@google.com>

For all direct access MSRs, disable the MSR interception explicitly.
svm_disable_intercept_for_msr() checks the new MSR filter and ensures that
KVM enables interception if userspace wants to filter the MSR.

This change is similar to the VMX change:
  d895f28ed6da ("KVM: VMX: Skip filter updates for MSRs that KVM is already intercepting")

Adopting in SVM to align the implementations.

Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Anish Ghulati <aghulati@google.com>
---
 arch/x86/kvm/svm/svm.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b982729ef7638..37b8683849ed2 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1025,17 +1025,21 @@ static void svm_msr_filter_changed(struct kvm_vcpu *vcpu)
 	u32 i;
 
 	/*
-	 * Set intercept permissions for all direct access MSRs again. They
-	 * will automatically get filtered through the MSR filter, so we are
-	 * back in sync after this.
+	 * Redo intercept permissions for MSRs that KVM is passing through to
+	 * the guest.  Disabling interception will check the new MSR filter and
+	 * ensure that KVM enables interception if usersepace wants to filter
+	 * the MSR.  MSRs that KVM is already intercepting don't need to be
+	 * refreshed since KVM is going to intercept them regardless of what
+	 * userspace wants.
 	 */
 	for (i = 0; direct_access_msrs[i].index != MSR_INVALID; i++) {
 		u32 msr = direct_access_msrs[i].index;
-		u32 read = !test_bit(i, svm->shadow_msr_intercept.read);
-		u32 write = !test_bit(i, svm->shadow_msr_intercept.write);
 
-		/* FIXME: Align the polarity of the bitmaps and params. */
-		set_msr_interception_bitmap(vcpu, svm->msrpm, msr, read, write);
+		if (!test_bit(i, svm->shadow_msr_intercept.read))
+			svm_disable_intercept_for_msr(vcpu, msr, MSR_TYPE_R);
+
+		if (!test_bit(i, svm->shadow_msr_intercept.write))
+			svm_disable_intercept_for_msr(vcpu, msr, MSR_TYPE_W);
 	}
 }
 
-- 
2.47.0.338.g60cca15819-goog