KVM: arm64: vgic-its: Rip out the global translation cache

The MSI injection fast path has been transitioned away from the global
translation cache. Rip it out.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240422200158.2606761-12-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: oupton

arch/arm64/kvm/vgic/vgic-init.c

@@ -53,7 +53,6 @@ void kvm_vgic_early_init(struct kvm *kvm)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
 
-	INIT_LIST_HEAD(&dist->lpi_translation_cache);
 	raw_spin_lock_init(&dist->lpi_list_lock);
 	xa_init_flags(&dist->lpi_xa, XA_FLAGS_LOCK_IRQ);
 }
@@ -305,9 +304,6 @@ int vgic_init(struct kvm *kvm)
 		}
 	}
 
-	if (vgic_has_its(kvm))
-		vgic_lpi_translation_cache_init(kvm);
-
 	/*
 	 * If we have GICv4.1 enabled, unconditionally request enable the
 	 * v4 support so that we get HW-accelerated vSGIs. Otherwise, only
@@ -361,9 +357,6 @@ static void kvm_vgic_dist_destroy(struct kvm *kvm)
 		dist->vgic_cpu_base = VGIC_ADDR_UNDEF;
 	}
 
-	if (vgic_has_its(kvm))
-		vgic_lpi_translation_cache_destroy(kvm);
-
 	if (vgic_supports_direct_msis(kvm))
 		vgic_v4_teardown(kvm);
 

arch/arm64/kvm/vgic/vgic-its.c

@@ -149,14 +149,6 @@ struct its_ite {
 	u32 event_id;
 };
 
-struct vgic_translation_cache_entry {
-	struct list_head	entry;
-	phys_addr_t		db;
-	u32			devid;
-	u32			eventid;
-	struct vgic_irq		*irq;
-};
-
 /**
  * struct vgic_its_abi - ITS abi ops and settings
  * @cte_esz: collection table entry size
@@ -568,96 +560,34 @@ static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
 				       struct vgic_irq *irq)
 {
 	unsigned long cache_key = vgic_its_cache_key(devid, eventid);
-	struct vgic_dist *dist = &kvm->arch.vgic;
-	struct vgic_translation_cache_entry *cte;
 	struct vgic_irq *old;
-	unsigned long flags;
-	phys_addr_t db;
 
 	/* Do not cache a directly injected interrupt */
 	if (irq->hw)
 		return;
 
-	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
-
-	if (unlikely(list_empty(&dist->lpi_translation_cache)))
-		goto out;
-
-	db = its->vgic_its_base + GITS_TRANSLATER;
-
-	/* Always reuse the last entry (LRU policy) */
-	cte = list_last_entry(&dist->lpi_translation_cache,
-			      typeof(*cte), entry);
-
-	/*
-	 * Caching the translation implies having an extra reference
-	 * to the interrupt, so drop the potential reference on what
-	 * was in the cache, and increment it on the new interrupt.
-	 */
-	if (cte->irq)
-		vgic_put_irq(kvm, cte->irq);
-
 	/*
 	 * The irq refcount is guaranteed to be nonzero while holding the
 	 * its_lock, as the ITE (and the reference it holds) cannot be freed.
 	 */
 	lockdep_assert_held(&its->its_lock);
-
-	/*
-	 * Yes, two references are necessary at the moment:
-	 *  - One for the global LPI translation cache
-	 *  - Another for the translation cache belonging to @its
-	 *
-	 * This will soon disappear.
-	 */
-	vgic_get_irq_kref(irq);
 	vgic_get_irq_kref(irq);
 
-	cte->db		= db;
-	cte->devid	= devid;
-	cte->eventid	= eventid;
-	cte->irq	= irq;
-
-	/* Move the new translation to the head of the list */
-	list_move(&cte->entry, &dist->lpi_translation_cache);
-	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
-
 	/*
-	 * The per-ITS cache is a perfect cache, so it may already have an
-	 * identical translation even if it were missing from the global
-	 * cache. Ensure we don't leak a reference if that is the case.
+	 * We could have raced with another CPU caching the same
+	 * translation behind our back, ensure we don't leak a
+	 * reference if that is the case.
 	 */
 	old = xa_store(&its->translation_cache, cache_key, irq, GFP_KERNEL_ACCOUNT);
 	if (old)
 		vgic_put_irq(kvm, old);
-
-out:
-	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
 }
 
 static void vgic_its_invalidate_cache(struct vgic_its *its)
 {
 	struct kvm *kvm = its->dev->kvm;
-	struct vgic_dist *dist = &kvm->arch.vgic;
-	struct vgic_translation_cache_entry *cte;
-	unsigned long flags, idx;
 	struct vgic_irq *irq;
-
-	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
-
-	list_for_each_entry(cte, &dist->lpi_translation_cache, entry) {
-		/*
-		 * If we hit a NULL entry, there is nothing after this
-		 * point.
-		 */
-		if (!cte->irq)
-			break;
-
-		vgic_put_irq(kvm, cte->irq);
-		cte->irq = NULL;
-	}
-
-	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+	unsigned long idx;
 
 	xa_for_each(&its->translation_cache, idx, irq) {
 		xa_erase(&its->translation_cache, idx);
@@ -1880,47 +1810,6 @@ static int vgic_register_its_iodev(struct kvm *kvm, struct vgic_its *its,
 	return ret;
 }
 
-/* Default is 16 cached LPIs per vcpu */
-#define LPI_DEFAULT_PCPU_CACHE_SIZE	16
-
-void vgic_lpi_translation_cache_init(struct kvm *kvm)
-{
-	struct vgic_dist *dist = &kvm->arch.vgic;
-	unsigned int sz;
-	int i;
-
-	if (!list_empty(&dist->lpi_translation_cache))
-		return;
-
-	sz = atomic_read(&kvm->online_vcpus) * LPI_DEFAULT_PCPU_CACHE_SIZE;
-
-	for (i = 0; i < sz; i++) {
-		struct vgic_translation_cache_entry *cte;
-
-		/* An allocation failure is not fatal */
-		cte = kzalloc(sizeof(*cte), GFP_KERNEL_ACCOUNT);
-		if (WARN_ON(!cte))
-			break;
-
-		INIT_LIST_HEAD(&cte->entry);
-		list_add(&cte->entry, &dist->lpi_translation_cache);
-	}
-}
-
-void vgic_lpi_translation_cache_destroy(struct kvm *kvm)
-{
-	struct vgic_dist *dist = &kvm->arch.vgic;
-	struct vgic_translation_cache_entry *cte, *tmp;
-
-	vgic_its_invalidate_all_caches(kvm);
-
-	list_for_each_entry_safe(cte, tmp,
-				 &dist->lpi_translation_cache, entry) {
-		list_del(&cte->entry);
-		kfree(cte);
-	}
-}
-
 #define INITIAL_BASER_VALUE						  \
 	(GIC_BASER_CACHEABILITY(GITS_BASER, INNER, RaWb)		| \
 	 GIC_BASER_CACHEABILITY(GITS_BASER, OUTER, SameAsInner)		| \
@@ -1953,8 +1842,6 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
 			kfree(its);
 			return ret;
 		}
-
-		vgic_lpi_translation_cache_init(dev->kvm);
 	}
 
 	mutex_init(&its->its_lock);

arch/arm64/kvm/vgic/vgic.h

@@ -335,8 +335,6 @@ int vgic_its_resolve_lpi(struct kvm *kvm, struct vgic_its *its,
 			 u32 devid, u32 eventid, struct vgic_irq **irq);
 struct vgic_its *vgic_msi_to_its(struct kvm *kvm, struct kvm_msi *msi);
 int vgic_its_inject_cached_translation(struct kvm *kvm, struct kvm_msi *msi);
-void vgic_lpi_translation_cache_init(struct kvm *kvm);
-void vgic_lpi_translation_cache_destroy(struct kvm *kvm);
 void vgic_its_invalidate_all_caches(struct kvm *kvm);
 
 /* GICv4.1 MMIO interface */

include/kvm/arm_vgic.h

@@ -286,9 +286,6 @@ struct vgic_dist {
 #define LPI_XA_MARK_DEBUG_ITER	XA_MARK_0
 	struct xarray		lpi_xa;
 
-	/* LPI translation cache */
-	struct list_head	lpi_translation_cache;
-
 	/* used by vgic-debug */
 	struct vgic_state_iter *iter;