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, 133 insertions, 0 deletions

diff --git a/arch/alpha/lib/memset.S b/arch/alpha/lib/memset.S
new file mode 100644
index 000000000..9075d6918
--- /dev/null
+++ b/arch/alpha/lib/memset.S
@@ -0,0 +1,133 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * linux/arch/alpha/lib/memset.S
+ *
+ * This is an efficient (and small) implementation of the C library "memset()"
+ * function for the alpha.
+ *
+ *	(C) Copyright 1996 Linus Torvalds
+ *
+ * This routine is "moral-ware": you are free to use it any way you wish, and
+ * the only obligation I put on you is a moral one: if you make any improvements
+ * to the routine, please send me your improvements for me to use similarly.
+ *
+ * The scheduling comments are according to the EV5 documentation (and done by 
+ * hand, so they might well be incorrect, please do tell me about it..)
+ */
+#include <linux/export.h>
+	.set noat
+	.set noreorder
+.text
+	.globl memset
+	.globl __memset
+	.globl ___memset
+	.globl __memset16
+	.globl __constant_c_memset
+
+	.ent ___memset
+.align 5
+___memset:
+	.frame $30,0,$26,0
+	.prologue 0
+
+	and $17,255,$1		/* E1 */
+	insbl $17,1,$17		/* .. E0 */
+	bis $17,$1,$17		/* E0 (p-c latency, next cycle) */
+	sll $17,16,$1		/* E1 (p-c latency, next cycle) */
+
+	bis $17,$1,$17		/* E0 (p-c latency, next cycle) */
+	sll $17,32,$1		/* E1 (p-c latency, next cycle) */
+	bis $17,$1,$17		/* E0 (p-c latency, next cycle) */
+	ldq_u $31,0($30)	/* .. E1 */
+
+.align 5
+__constant_c_memset:
+	addq $18,$16,$6		/* E0 */
+	bis $16,$16,$0		/* .. E1 */
+	xor $16,$6,$1		/* E0 */
+	ble $18,end		/* .. E1 */
+
+	bic $1,7,$1		/* E0 */
+	beq $1,within_one_quad	/* .. E1 (note EV5 zero-latency forwarding) */
+	and $16,7,$3		/* E0 */
+	beq $3,aligned		/* .. E1 (note EV5 zero-latency forwarding) */
+
+	ldq_u $4,0($16)		/* E0 */
+	bis $16,$16,$5		/* .. E1 */
+	insql $17,$16,$2	/* E0 */
+	subq $3,8,$3		/* .. E1 */
+
+	addq $18,$3,$18		/* E0	$18 is new count ($3 is negative) */
+	mskql $4,$16,$4		/* .. E1 (and possible load stall) */
+	subq $16,$3,$16		/* E0 	$16 is new aligned destination */
+	bis $2,$4,$1		/* .. E1 */
+
+	bis $31,$31,$31		/* E0 */
+	ldq_u $31,0($30)	/* .. E1 */
+	stq_u $1,0($5)		/* E0 */
+	bis $31,$31,$31		/* .. E1 */
+
+.align 4
+aligned:
+	sra $18,3,$3		/* E0 */
+	and $18,7,$18		/* .. E1 */
+	bis $16,$16,$5		/* E0 */
+	beq $3,no_quad		/* .. E1 */
+
+.align 3
+loop:
+	stq $17,0($5)		/* E0 */
+	subq $3,1,$3		/* .. E1 */
+	addq $5,8,$5		/* E0 */
+	bne $3,loop		/* .. E1 */
+
+no_quad:
+	bis $31,$31,$31		/* E0 */
+	beq $18,end		/* .. E1 */
+	ldq $7,0($5)		/* E0 */
+	mskqh $7,$6,$2		/* .. E1 (and load stall) */
+
+	insqh $17,$6,$4		/* E0 */
+	bis $2,$4,$1		/* .. E1 */
+	stq $1,0($5)		/* E0 */
+	ret $31,($26),1		/* .. E1 */
+
+.align 3
+within_one_quad:
+	ldq_u $1,0($16)		/* E0 */
+	insql $17,$16,$2	/* E1 */
+	mskql $1,$16,$4		/* E0 (after load stall) */
+	bis $2,$4,$2		/* E0 */
+
+	mskql $2,$6,$4		/* E0 */
+	mskqh $1,$6,$2		/* .. E1 */
+	bis $2,$4,$1		/* E0 */
+	stq_u $1,0($16)		/* E0 */
+
+end:
+	ret $31,($26),1		/* E1 */
+	.end ___memset
+EXPORT_SYMBOL(___memset)
+EXPORT_SYMBOL(__constant_c_memset)
+
+	.align 5
+	.ent __memset16
+__memset16:
+	.prologue 0
+
+	inswl $17,0,$1		/* E0 */
+	inswl $17,2,$2		/* E0 */
+	inswl $17,4,$3		/* E0 */
+	or $1,$2,$1		/* .. E1 */
+	inswl $17,6,$4		/* E0 */
+	or $1,$3,$1		/* .. E1 */
+	or $1,$4,$17		/* E0 */
+	br __constant_c_memset	/* .. E1 */
+
+	.end __memset16
+EXPORT_SYMBOL(__memset16)
+
+memset = ___memset
+__memset = ___memset
+	EXPORT_SYMBOL(memset)
+	EXPORT_SYMBOL(__memset)