Merge tag 'kvm-x86-fixes-6.11-rcN' of https://github.com/kvm-x86/linux into kvm-master

KVM x86 fixes for 6.11

 - Fixup missed comments from the REMOVED_SPTE=>FROZEN_SPTE rename.

 - Ensure a root is successfully loaded when pre-faulting SPTEs.

 - Grab kvm->srcu when handling KVM_SET_VCPU_EVENTS to guard against accessing
   memslots if toggling SMM happens to force a VM-Exit.

 - Emulate MSR_{FS,GS}_BASE on SVM even though interception is always disabled,
   so that KVM does the right thing if KVM's emulator encounters {RD,WR}MSR.

 - Explicitly clear BUS_LOCK_DETECT from KVM's caps on AMD, as KVM doesn't yet
   virtualize BUS_LOCK_DETECT on AMD.

 - Cleanup the help message for CONFIG_KVM_AMD_SEV, and call out that KVM now
   supports SEV-SNP too.

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 83478deada3b..98fa0f382480 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -28,6 +28,7 @@
 #include <linux/btrfs.h>
 #include <linux/security.h>
 #include <linux/fs_parser.h>
+#include <linux/swap.h>
 #include "messages.h"
 #include "delayed-inode.h"
 #include "ctree.h"
@@ -2401,7 +2402,13 @@ static long btrfs_nr_cached_objects(struct super_block *sb, struct shrink_contro
 
 	trace_btrfs_extent_map_shrinker_count(fs_info, nr);
 
-	return nr;
+	/*
+	 * Only report the real number for DEBUG builds, as there are reports of
+	 * serious performance degradation caused by too frequent shrinks.
+	 */
+	if (IS_ENABLED(CONFIG_BTRFS_DEBUG))
+		return nr;
+	return 0;
 }
 
 static long btrfs_free_cached_objects(struct super_block *sb, struct shrink_control *sc)
@@ -2409,6 +2416,15 @@ static long btrfs_free_cached_objects(struct super_block *sb, struct shrink_cont
 	const long nr_to_scan = min_t(unsigned long, LONG_MAX, sc->nr_to_scan);
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
 
+	/*
+	 * We may be called from any task trying to allocate memory and we don't
+	 * want to slow it down with scanning and dropping extent maps. It would
+	 * also cause heavy lock contention if many tasks concurrently enter
+	 * here. Therefore only allow kswapd tasks to scan and drop extent maps.
+	 */
+	if (!current_is_kswapd())
+		return 0;
+
 	return btrfs_free_extent_maps(fs_info, nr_to_scan);
 }