Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Maxim Levitsky <mlevitsk@redhat.com>
To:     kvm@vger.kernel.org
Cc:     Wanpeng Li <wanpengli@tencent.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Jim Mattson <jmattson@google.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Joerg Roedel <joro@8bytes.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        linux-kernel@vger.kernel.org, Maxim Levitsky <mlevitsk@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        Borislav Petkov <bp@alien8.de>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH 6/7] KVM: x86: disable preemption around the call to kvm_arch_vcpu_{un|}blocking
Date:   Mon,  6 Jun 2022 21:08:28 +0300
Message-Id: <20220606180829.102503-7-mlevitsk@redhat.com>
In-Reply-To: <20220606180829.102503-1-mlevitsk@redhat.com>
References: <20220606180829.102503-1-mlevitsk@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@redhat.com>
---
 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 5e511fcec80d7..642dba492c65d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3337,9 +3337,11 @@ 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);
 
@@ -3349,9 +3351,11 @@ 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;
 
-- 
2.26.3