linux-kernel - [PATCH 5.18 14/35] KVM: x86: disable preemption around the call to kvm_arch_vcpu

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Message-Id: <20220809175515.577225397@linuxfoundation.org>
Date:   Tue,  9 Aug 2022 20:00:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.18 14/35] KVM: x86: disable preemption around the call to kvm_arch_vcpu_{un|}blocking

From: Maxim Levitsky <mlevitsk@...hat.com>

[ Upstream commit 18869f26df1a11ed11031dfb7392bc7d774062e8 ]

On SVM, if preemption happens right after the call to finish_rcuwait
but before call to kvm_arch_vcpu_unblocking on SVM/AVIC, it itself
will re-enable AVIC, and then we will try to re-enable it again
in kvm_arch_vcpu_unblocking which will lead to a warning
in __avic_vcpu_load.

The same problem can happen if the vCPU is preempted right after the call
to kvm_arch_vcpu_blocking but before the call to prepare_to_rcuwait
and in this case, we will end up with AVIC enabled during sleep -
Ooops.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
Message-Id: <20220606180829.102503-7-mlevitsk@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 virt/kvm/kvm_main.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 24cb37d19c63..7f1d19689701 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3327,9 +3327,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 
 	vcpu->stat.generic.blocking = 1;
 
+	preempt_disable();
 	kvm_arch_vcpu_blocking(vcpu);
-
 	prepare_to_rcuwait(wait);
+	preempt_enable();
+
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
 
@@ -3339,9 +3341,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu)
 		waited = true;
 		schedule();
 	}
-	finish_rcuwait(wait);
 
+	preempt_disable();
+	finish_rcuwait(wait);
 	kvm_arch_vcpu_unblocking(vcpu);
+	preempt_enable();
 
 	vcpu->stat.generic.blocking = 0;
 
-- 
2.35.1