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FAILED: patch "[PATCH] KVM: SVM: Set target pCPU during IRTE update if target vCPU" failed to apply to 5.15-stable tree

PATCH [email protected] 1 participant 1 message Sep 16, 2023

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The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x f3cebc75e7425d6949d726bb8e937095b0aef025
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023091655-resize-playmate-ac62@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

f3cebc75e742 ("KVM: SVM: Set target pCPU during IRTE update if target vCPU is running") 4c08e737f056 ("KVM: SVM: Take and hold ir_list_lock when updating vCPU's Physical ID entry") 935a7333958e ("KVM: SVM: Drop AVIC's intermediate avic_set_running() helper") 782f64558de7 ("KVM: SVM: Skip AVIC and IRTE updates when loading blocking vCPU") af52f5aa5c1b ("KVM: SVM: Use kvm_vcpu_is_blocking() in AVIC load to handle preemption") e422b8896948 ("KVM: SVM: Remove unnecessary APICv/AVIC update in vCPU unblocking path") 7cfc5c653b07 ("KVM: fix avic_set_running for preemptable kernels")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f3cebc75e7425d6949d726bb8e937095b0aef025 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Tue, 8 Aug 2023 16:31:32 -0700
Subject: [PATCH] KVM: SVM: Set target pCPU during IRTE update if target vCPU
is running

Update the target pCPU for IOMMU doorbells when updating IRTE routing if KVM is actively running the associated vCPU. KVM currently only updates the pCPU when loading the vCPU (via avic_vcpu_load()), and so doorbell events will be delayed until the vCPU goes through a put+load cycle (which might very well "never" happen for the lifetime of the VM).

To avoid inserting a stale pCPU, e.g. due to racing between updating IRTE routing and vCPU load/put, get the pCPU information from the vCPU's Physical APIC ID table entry (a.k.a. avic_physical_id_cache in KVM) and update the IRTE while holding ir_list_lock. Add comments with --verbose enabled to explain exactly what is and isn't protected by ir_list_lock.

Fixes 411b44ba80ab ("svm: Implements update_pi_irte hook to setup posted interrupt")
Reported-by dengqiao.joey <[email protected]>
Cc [email protected]
Cc Alejandro Jimenez <[email protected]>
Cc Joao Martins <[email protected]>
Cc Maxim Levitsky <[email protected]>
Cc Suravee Suthikulpanit <[email protected]>
Tested-by Alejandro Jimenez <[email protected]>
Reviewed-by Joao Martins <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Sean Christopherson <[email protected]>
arch/x86/kvm/svm/avic.c +28 -0
index 8e041b215ddb..2092db892d7d 100644
@@ -791,6 +791,7 @@ 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,

@@ -824,6 +825,18 @@ static int svm_ir_list_add(struct vcpu_svm *svm, struct amd_iommu_pi_data *pi)
 	ir->data = pi->ir_data;
 
 	spin_lock_irqsave(&svm->ir_list_lock, flags);
+
+	/*
+	 * Update the target pCPU for IOMMU doorbells if the vCPU is running.
+	 * If the vCPU is NOT running, i.e. is blocking or scheduled out, KVM
+	 * 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);
+
 	list_add(&ir->node, &svm->ir_list);
 	spin_unlock_irqrestore(&svm->ir_list_lock, flags);
 out:

@@ -1031,6 +1044,13 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (kvm_vcpu_is_blocking(vcpu))
 		return;
 
+	/*
+	 * Grab the per-vCPU interrupt remapping lock even if the VM doesn't
+	 * _currently_ have assigned devices, as that can change.  Holding
+	 * ir_list_lock ensures that either svm_ir_list_add() will consume
+	 * up-to-date entry information, or that this task will wait until
+	 * svm_ir_list_add() completes to set the new target pCPU.
+	 */
 	spin_lock_irqsave(&svm->ir_list_lock, flags);
 
 	entry = READ_ONCE(*(svm->avic_physical_id_cache));

@@ -1067,6 +1087,14 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
 	if (!(entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK))
 		return;
 
+	/*
+	 * Take and hold the per-vCPU interrupt remapping lock while updating
+	 * the Physical ID entry even though the lock doesn't protect against
+	 * multiple writers (see above).  Holding ir_list_lock ensures that
+	 * either svm_ir_list_add() will consume up-to-date entry information,
+	 * or that this task will wait until svm_ir_list_add() completes to
+	 * mark the vCPU as not running.
+	 */
 	spin_lock_irqsave(&svm->ir_list_lock, flags);
 
 	avic_update_iommu_vcpu_affinity(vcpu, -1, 0);