git: fb0bdbea2ed4 - main - cache: avoid hardcoded zone alignment

The branch main has been updated by brooks:

URL: https://cgit.FreeBSD.org/src/commit/?id=fb0bdbea2ed4f63ef07061313f8cef89a3d73579

commit fb0bdbea2ed4f63ef07061313f8cef89a3d73579
Author:     Brooks Davis <brooks@FreeBSD.org>
AuthorDate: 2026-01-09 14:15:22 +0000
Commit:     Brooks Davis <brooks@FreeBSD.org>
CommitDate: 2026-01-09 14:15:22 +0000

    cache: avoid hardcoded zone alignment
    
    Previously, this was underaligned on CHERI system where pointers are
    larger than time_t.
    
    Use the alignment of struct namecache_ts which picks up time_t via strut
    timespec and pointers via struct namecache.  This arguably overaligns
    cache_zone_small and cache_zone_large on i386 kernels, but I suspect the
    actual microarchitectures most i386 binaries are run on do better with
    64-bit alignment.
    
    Reviewed by:    olce, markj
    Effort:         CHERI upstreaming
    Sponsored by:   Innovate UK
    Fixes:          cf8ac0de8150 ("cache: reduce zone alignment to 8 bytes")
    Differential Revision:  https://reviews.freebsd.org/D54376
---
 sys/kern/vfs_cache.c | 46 ++++++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 22 deletions(-)

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 557e451f9a45..c5abc1c8b9b7 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -384,14 +384,10 @@ struct	namecache {
 };
 
 /*
- * struct namecache_ts repeats struct namecache layout up to the
- * nc_nlen member.
  * struct namecache_ts is used in place of struct namecache when time(s) need
  * to be stored.  The nc_dotdottime field is used when a cache entry is mapping
  * both a non-dotdot directory name plus dotdot for the directory's
  * parent.
- *
- * See below for alignment requirement.
  */
 struct	namecache_ts {
 	struct	timespec nc_time;	/* timespec provided by fs */
@@ -404,12 +400,10 @@ struct	namecache_ts {
 TAILQ_HEAD(cache_freebatch, namecache);
 
 /*
- * At least mips n32 performs 64-bit accesses to timespec as found
- * in namecache_ts and requires them to be aligned. Since others
- * may be in the same spot suffer a little bit and enforce the
- * alignment for everyone. Note this is a nop for 64-bit platforms.
+ * Ensure all zones are sufficently aligned to hold both
+ * struct namecache and struct namecache_ts.
  */
-#define CACHE_ZONE_ALIGNMENT	UMA_ALIGNOF(time_t)
+#define CACHE_ZONE_ALIGN_MASK	UMA_ALIGNOF(struct namecache_ts)
 
 /*
  * TODO: the initial value of CACHE_PATH_CUTOFF was inherited from the
@@ -432,15 +426,23 @@ TAILQ_HEAD(cache_freebatch, namecache);
 #define	CACHE_LARGE_PAD		2
 #endif
 
-#define CACHE_ZONE_SMALL_SIZE		(offsetof(struct namecache, nc_name) + CACHE_PATH_CUTOFF + 1)
-#define CACHE_ZONE_SMALL_TS_SIZE	(offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_SMALL_SIZE)
-#define CACHE_ZONE_LARGE_SIZE		(offsetof(struct namecache, nc_name) + NAME_MAX + 1 + CACHE_LARGE_PAD)
-#define CACHE_ZONE_LARGE_TS_SIZE	(offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_LARGE_SIZE)
-
-_Static_assert((CACHE_ZONE_SMALL_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
-_Static_assert((CACHE_ZONE_SMALL_TS_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
-_Static_assert((CACHE_ZONE_LARGE_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
-_Static_assert((CACHE_ZONE_LARGE_TS_SIZE % (CACHE_ZONE_ALIGNMENT + 1)) == 0, "bad zone size");
+#define CACHE_ZONE_SMALL_SIZE						\
+    (offsetof(struct namecache, nc_name) + CACHE_PATH_CUTOFF + 1)
+#define CACHE_ZONE_SMALL_TS_SIZE					\
+    (offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_SMALL_SIZE)
+#define CACHE_ZONE_LARGE_SIZE						\
+    (offsetof(struct namecache, nc_name) + NAME_MAX + 1 + CACHE_LARGE_PAD)
+#define CACHE_ZONE_LARGE_TS_SIZE					\
+    (offsetof(struct namecache_ts, nc_nc) + CACHE_ZONE_LARGE_SIZE)
+
+_Static_assert((CACHE_ZONE_SMALL_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
+    "bad zone size");
+_Static_assert((CACHE_ZONE_SMALL_TS_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
+    "bad zone size");
+_Static_assert((CACHE_ZONE_LARGE_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
+    "bad zone size");
+_Static_assert((CACHE_ZONE_LARGE_TS_SIZE % (CACHE_ZONE_ALIGN_MASK + 1)) == 0,
+    "bad zone size");
 
 #define	nc_vp		n_un.nu_vp
 #define	nc_neg		n_un.nu_neg
@@ -2785,13 +2787,13 @@ nchinit(void *dummy __unused)
 	u_int i;
 
 	cache_zone_small = uma_zcreate("S VFS Cache", CACHE_ZONE_SMALL_SIZE,
-	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
 	cache_zone_small_ts = uma_zcreate("STS VFS Cache", CACHE_ZONE_SMALL_TS_SIZE,
-	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
 	cache_zone_large = uma_zcreate("L VFS Cache", CACHE_ZONE_LARGE_SIZE,
-	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
 	cache_zone_large_ts = uma_zcreate("LTS VFS Cache", CACHE_ZONE_LARGE_TS_SIZE,
-	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGNMENT, UMA_ZONE_ZINIT);
+	    NULL, NULL, NULL, NULL, CACHE_ZONE_ALIGN_MASK, UMA_ZONE_ZINIT);
 
 	VFS_SMR_ZONE_SET(cache_zone_small);
 	VFS_SMR_ZONE_SET(cache_zone_small_ts);