linux-kernel - [PATCH 5/7] KVM: x86: disable preemption while updating apicv inhibition

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Date:   Mon,  6 Jun 2022 21:08:27 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5/7] KVM: x86: disable preemption while updating apicv inhibition

Currently nothing prevents preemption in kvm_vcpu_update_apicv.

On SVM, If the preemption happens after we update the
vcpu->arch.apicv_active, the preemption itself will
'update' the inhibition since the AVIC will be first disabled
on vCPU unload and then enabled, when the current task
is loaded again.

Then we will try to update it again, which will lead to a warning
in __avic_vcpu_load, that the AVIC is already enabled.

Fix this by disabling preemption in this code.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2db6f0373fa3f..9bbe6144d82ae 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9893,6 +9893,7 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 		return;
 
 	down_read(&vcpu->kvm->arch.apicv_update_lock);
+	preempt_disable();
 
 	activate = kvm_vcpu_apicv_activated(vcpu);
 
@@ -9913,6 +9914,7 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 		kvm_make_request(KVM_REQ_EVENT, vcpu);
 
 out:
+	preempt_enable();
 	up_read(&vcpu->kvm->arch.apicv_update_lock);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);
-- 
2.26.3