linux-kernel - [PATCH 1/4] KVM: nSVM: do not change host intercepts while nested VM is running

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Date:   Thu,  5 Mar 2020 11:13:44 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     cavery@...hat.com, vkuznets@...hat.com, jan.kiszka@...mens.com,
        wei.huang2@....com
Subject: [PATCH 1/4] KVM: nSVM: do not change host intercepts while nested VM is running

Instead of touching the host intercepts so that the bitwise OR in
recalc_intercepts just works, mask away uninteresting intercepts
directly in recalc_intercepts.

This is cleaner and keeps the logic in one place even for intercepts
that can change even while L2 is running.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 247e31d21b96..14cb5c194008 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -519,10 +519,24 @@ static void recalc_intercepts(struct vcpu_svm *svm)
 	h = &svm->nested.hsave->control;
 	g = &svm->nested;
 
-	c->intercept_cr = h->intercept_cr | g->intercept_cr;
-	c->intercept_dr = h->intercept_dr | g->intercept_dr;
-	c->intercept_exceptions = h->intercept_exceptions | g->intercept_exceptions;
-	c->intercept = h->intercept | g->intercept;
+	c->intercept_cr = h->intercept_cr;
+	c->intercept_dr = h->intercept_dr;
+	c->intercept_exceptions = h->intercept_exceptions;
+	c->intercept = h->intercept;
+
+	if (svm->vcpu.arch.hflags & HF_VINTR_MASK) {
+		/* We only want the cr8 intercept bits of L1 */
+		c->intercept_cr &= ~(1U << INTERCEPT_CR8_READ);
+		c->intercept_cr &= ~(1U << INTERCEPT_CR8_WRITE);
+	}
+
+	/* We don't want to see VMMCALLs from a nested guest */
+	c->intercept &= ~(1ULL << INTERCEPT_VMMCALL);
+
+	c->intercept_cr |= g->intercept_cr;
+	c->intercept_dr |= g->intercept_dr;
+	c->intercept_exceptions |= g->intercept_exceptions;
+	c->intercept |= g->intercept;
 }
 
 static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)
@@ -3590,15 +3604,6 @@ static void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
 	else
 		svm->vcpu.arch.hflags &= ~HF_VINTR_MASK;
 
-	if (svm->vcpu.arch.hflags & HF_VINTR_MASK) {
-		/* We only want the cr8 intercept bits of the guest */
-		clr_cr_intercept(svm, INTERCEPT_CR8_READ);
-		clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
-	}
-
-	/* We don't want to see VMMCALLs from a nested guest */
-	clr_intercept(svm, INTERCEPT_VMMCALL);
-
 	svm->vcpu.arch.tsc_offset += nested_vmcb->control.tsc_offset;
 	svm->vmcb->control.tsc_offset = svm->vcpu.arch.tsc_offset;
 
-- 
1.8.3.1