linux-kernel - [PATCH v3 3/4] x86: KVM: don't read physical ID table entry in avic_pi_update

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Date:   Mon,  2 Oct 2023 14:57:22 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH v3 3/4] x86: KVM: don't read physical ID table entry in avic_pi_update_irte()

Change AVIC's code to use vcpu->loaded and vcpu->cpu instead of reading
back the cpu and 'is_running' bit from the avic's physical id entry.

Once AVIC's IPI virtualization is made optional, the 'is_running'
bit might always be false regardless if a vCPU is running or not.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/avic.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 4c75ca15999fcd4..bdab28005ad3405 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -791,7 +791,6 @@ static int svm_ir_list_add(struct vcpu_svm *svm, struct amd_iommu_pi_data *pi)
 	int ret = 0;
 	unsigned long flags;
 	struct amd_svm_iommu_ir *ir;
-	u64 entry;
 
 	/**
 	 * In some cases, the existing irte is updated and re-set,
@@ -832,10 +831,11 @@ static int svm_ir_list_add(struct vcpu_svm *svm, struct amd_iommu_pi_data *pi)
 	 * will update the pCPU info when the vCPU awkened and/or scheduled in.
 	 * See also avic_vcpu_load().
 	 */
-	entry = READ_ONCE(*(svm->avic_physical_id_cache));
-	if (entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK)
-		amd_iommu_update_ga(entry & AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK,
-				    true, pi->ir_data);
+	if (READ_ONCE(svm->vcpu.loaded)) {
+		/* Ensure that the vcpu->loaded is read before the vcpu->cpu */
+		smp_rmb();
+		amd_iommu_update_ga(READ_ONCE(svm->vcpu.cpu), true, pi->ir_data);
+	}
 
 	list_add(&ir->node, &svm->ir_list);
 	spin_unlock_irqrestore(&svm->ir_list_lock, flags);
-- 
2.26.3