KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/arch/alpha/lib/strcat.S b/arch/alpha/lib/strcat.S
new file mode 100644
index 000000000..62b90ebbc
--- /dev/null
+++ b/arch/alpha/lib/strcat.S
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * arch/alpha/lib/strcat.S
+ * Contributed by Richard Henderson (rth@tamu.edu)
+ *
+ * Append a null-terminated string from SRC to DST.
+ */
+#include <linux/export.h>
+
+	.text
+
+	.align 3
+	.globl strcat
+	.ent strcat
+strcat:
+	.frame $30, 0, $26
+	.prologue 0
+
+	mov	$16, $0		# set up return value
+
+	/* Find the end of the string.  */
+
+	ldq_u   $1, 0($16)	# load first quadword (a0 may be misaligned)
+	lda     $2, -1
+	insqh   $2, $16, $2
+	andnot  $16, 7, $16
+	or      $2, $1, $1
+	cmpbge  $31, $1, $2	# bits set iff byte == 0
+	bne     $2, $found
+
+$loop:	ldq     $1, 8($16)
+	addq    $16, 8, $16
+	cmpbge  $31, $1, $2
+	beq     $2, $loop
+
+$found:	negq    $2, $3		# clear all but least set bit
+	and     $2, $3, $2
+
+	and     $2, 0xf0, $3	# binary search for that set bit
+	and	$2, 0xcc, $4
+	and	$2, 0xaa, $5
+	cmovne	$3, 4, $3
+	cmovne	$4, 2, $4
+	cmovne	$5, 1, $5
+	addq	$3, $4, $3
+	addq	$16, $5, $16
+	addq	$16, $3, $16
+
+	/* Now do the append.  */
+
+	mov	$26, $23
+	br	__stxcpy
+
+	.end strcat
+EXPORT_SYMBOL(strcat);