linux-kernel - [PATCHv4 01/11] KVM: nSVM: Don't sync vmcb02 V_IRQ back to vmcb12 if KVM (L0) is intercepting VINTR

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Date:   Mon, 27 Feb 2023 14:10:06 +0530
From:   Santosh Shukla <santosh.shukla@....com>
To:     <kvm@...r.kernel.org>, <seanjc@...gle.com>
CC:     <pbonzini@...hat.com>, <jmattson@...gle.com>, <joro@...tes.org>,
        <linux-kernel@...r.kernel.org>, <mail@...iej.szmigiero.name>,
        <mlevitsk@...hat.com>, <thomas.lendacky@....com>,
        <vkuznets@...hat.com>
Subject: [PATCHv4 01/11] KVM: nSVM: Don't sync vmcb02 V_IRQ back to vmcb12 if KVM (L0) is intercepting VINTR

From: Santosh Shukla <Santosh.Shukla@....com>

Don't sync vmcb02 V_IRQ back to vmcb12 if KVM (L0) is intercepting
virtual interrupts in order to request an interrupt window, as KVM
has usurped vmcb02's int_ctl.  If an interrupt window opens before
the next VM-Exit, svm_clear_vintr() will restore vmcb12's int_ctl.
If no window opens, V_IRQ will be correctly preserved in vmcb12's
int_ctl (because it was never recognized while L2 was running).

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Santosh Shukla <Santosh.Shukla@....com>
---
v4:
https://lore.kernel.org/all/Y9hybI65So5X2LFg@google.com/
suggested by Sean.

 arch/x86/kvm/svm/nested.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 05d38944a6c0..fbade158d368 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -416,18 +416,17 @@ void nested_sync_control_from_vmcb02(struct vcpu_svm *svm)
 
 	/* Only a few fields of int_ctl are written by the processor.  */
 	mask = V_IRQ_MASK | V_TPR_MASK;
-	if (!(svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK) &&
-	    svm_is_intercept(svm, INTERCEPT_VINTR)) {
-		/*
-		 * In order to request an interrupt window, L0 is usurping
-		 * svm->vmcb->control.int_ctl and possibly setting V_IRQ
-		 * even if it was clear in L1's VMCB.  Restoring it would be
-		 * wrong.  However, in this case V_IRQ will remain true until
-		 * interrupt_window_interception calls svm_clear_vintr and
-		 * restores int_ctl.  We can just leave it aside.
-		 */
+	/*
+	 * Don't sync vmcb02 V_IRQ back to vmcb12 if KVM (L0) is intercepting
+	 * virtual interrupts in order to request an interrupt window, as KVM
+	 * has usurped vmcb02's int_ctl.  If an interrupt window opens before
+	 * the next VM-Exit, svm_clear_vintr() will restore vmcb12's int_ctl.
+	 * If no window opens, V_IRQ will be correctly preserved in vmcb12's
+	 * int_ctl (because it was never recognized while L2 was running).
+	 */
+	if (svm_is_intercept(svm, INTERCEPT_VINTR) &&
+	   !test_bit(INTERCEPT_VINTR, (unsigned long *)svm->nested.ctl.intercepts))
 		mask &= ~V_IRQ_MASK;
-	}
 
 	if (nested_vgif_enabled(svm))
 		mask |= V_GIF_MASK;
-- 
2.25.1