Use the cached dc zva length in arm64 memset

On boot we cache the length the 'dc zva' instruction will zero. Use
this in the memset function to decide when to use it. As the cached
value is in .bss it will be zero on boot so memset is safe to use
before the value has been read.

Sponsored by:	The FreeBSD Foundation

(cherry picked from commit 7d90ce7cae63a8121da0acc3ce36a713a98d6033)

1 files changed, 5 insertions, 43 deletions

diff --git a/sys/arm64/arm64/memset.S b/sys/arm64/arm64/memset.S
index aaa196d35278..ec434493ce13 100644
--- a/sys/arm64/arm64/memset.S
+++ b/sys/arm64/arm64/memset.S
@@ -33,17 +33,6 @@
 
 #include <machine/asm.h>
 
-
-/* By default we assume that the DC instruction can be used to zero
-   data blocks more efficiently.  In some circumstances this might be
-   unsafe, for example in an asymmetric multiprocessor environment with
-   different DC clear lengths (neither the upper nor lower lengths are
-   safe to use).  The feature can be disabled by defining DONT_USE_DC.
-
-   If code may be run in a virtualized environment, then define
-   MAYBE_VIRT.  This will cause the code to cache the system register
-   values rather than re-reading them each call.  */
-
 #define dstin		x0
 #define val		w1
 #define count		x2
@@ -143,7 +132,6 @@ ENTRY(memset)
 	b.ne	.Ltail63
 	ret
 
-#ifndef DONT_USE_DC
 	/* For zeroing memory, check to see if we can use the ZVA feature to
 	 * zero entire 'cache' lines.  */
 .Lzero_mem:
@@ -163,30 +151,11 @@ ENTRY(memset)
 	 * the line-clear code.  */
 	cmp	count, #128
 	b.lt	.Lnot_short
-#ifdef MAYBE_VIRT
-	/* For efficiency when virtualized, we cache the ZVA capability.  */
-	adrp	tmp2, .Lcache_clear
-	ldr	zva_len, [tmp2, #:lo12:.Lcache_clear]
-	tbnz	zva_len, #31, .Lnot_short
-	cbnz	zva_len, .Lzero_by_line
-	mrs	tmp1, dczid_el0
-	tbz	tmp1, #4, 1f
-	/* ZVA not available.  Remember this for next time.  */
-	mov	zva_len, #~0
-	str	zva_len, [tmp2, #:lo12:.Lcache_clear]
-	b	.Lnot_short
-1:
-	mov	tmp3w, #4
-	and	zva_len, tmp1w, #15	/* Safety: other bits reserved.  */
-	lsl	zva_len, tmp3w, zva_len
-	str	zva_len, [tmp2, #:lo12:.Lcache_clear]
-#else
-	mrs	tmp1, dczid_el0
-	tbnz	tmp1, #4, .Lnot_short
-	mov	tmp3w, #4
-	and	zva_len, tmp1w, #15	/* Safety: other bits reserved.  */
-	lsl	zva_len, tmp3w, zva_len
-#endif
+
+	adrp	tmp2, dczva_line_size
+	add	tmp2, tmp2, :lo12:dczva_line_size
+	ldr	zva_len, [tmp2]
+	cbz	zva_len, .Lnot_short
 
 .Lzero_by_line:
 	/* Compute how far we need to go to become suitably aligned.  We're
@@ -225,11 +194,4 @@ ENTRY(memset)
 	ands	count, count, zva_bits_x
 	b.ne	.Ltail_maybe_long
 	ret
-#ifdef MAYBE_VIRT
-	.bss
-	.p2align 2
-.Lcache_clear:
-	.space 4
-#endif
-#endif /* DONT_USE_DC */
 END(memset)