Merge branch 'kvm-5.20-early-patches' into HEAD

1 files changed, 9 insertions, 0 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 44c47670447a..7f79abdbd68d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -724,6 +724,15 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	kvm->mn_active_invalidate_count++;
 	spin_unlock(&kvm->mn_invalidate_lock);
 
+	/*
+	 * Invalidate pfn caches _before_ invalidating the secondary MMUs, i.e.
+	 * before acquiring mmu_lock, to avoid holding mmu_lock while acquiring
+	 * each cache's lock.  There are relatively few caches in existence at
+	 * any given time, and the caches themselves can check for hva overlap,
+	 * i.e. don't need to rely on memslot overlap checks for performance.
+	 * Because this runs without holding mmu_lock, the pfn caches must use
+	 * mn_active_invalidate_count (see above) instead of mmu_notifier_count.
+	 */
 	gfn_to_pfn_cache_invalidate_start(kvm, range->start, range->end,
 					  hva_range.may_block);