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>

2 files changed, 81 insertions, 0 deletions

diff --git a/arch/m68k/tools/amiga/Makefile b/arch/m68k/tools/amiga/Makefile
new file mode 100644
index 000000000..e6425b367
--- /dev/null
+++ b/arch/m68k/tools/amiga/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CC =		m68k-cbm-amigados-gcc
+CFLAGS =	-Wall -O2
+
+
+All:		dmesg
+
+
+dmesg:		dmesg.c
+		$(CC) $(CFLAGS) -o dmesg dmesg.c -noixemul
+
diff --git a/arch/m68k/tools/amiga/dmesg.c b/arch/m68k/tools/amiga/dmesg.c
new file mode 100644
index 000000000..f8005a7ef
--- /dev/null
+++ b/arch/m68k/tools/amiga/dmesg.c
@@ -0,0 +1,69 @@
+/*
+ *  linux/arch/m68k/tools/amiga/dmesg.c -- Retrieve the kernel messages stored
+ *					   in Chip RAM with the kernel command
+ *					   line option `debug=mem'.
+ *
+ *  © Copyright 1996 by Geert Uytterhoeven <geert@linux-m68k.org>
+ *
+ *
+ *  Usage:
+ *
+ *	dmesg
+ *	dmesg <CHIPMEM_END>
+ *
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+#define CHIPMEM_START	0x00000000
+#define CHIPMEM_END	0x00200000	/* overridden by argv[1] */
+
+#define SAVEKMSG_MAGIC1	0x53415645	/* 'SAVE' */
+#define SAVEKMSG_MAGIC2	0x4B4D5347	/* 'KMSG' */
+
+struct savekmsg {
+    u_long magic1;	/* SAVEKMSG_MAGIC1 */
+    u_long magic2;	/* SAVEKMSG_MAGIC2 */
+    u_long magicptr;	/* address of magic1 */
+    u_long size;
+    char data[];
+};
+
+
+int main(int argc, char *argv[])
+{
+    u_long start = CHIPMEM_START, end = CHIPMEM_END, p;
+    int found = 0;
+    struct savekmsg *m = NULL;
+
+    if (argc >= 2)
+	end = strtoul(argv[1], NULL, 0);
+    printf("Searching for SAVEKMSG magic...\n");
+    for (p = start; p <= end-sizeof(struct savekmsg); p += 4) {
+	m = (struct savekmsg *)p;
+	if ((m->magic1 == SAVEKMSG_MAGIC1) && (m->magic2 == SAVEKMSG_MAGIC2) &&
+	    (m->magicptr == p)) {
+	    found = 1;
+	    break;
+	}
+    }
+    if (!found)
+	printf("Not found\n");
+    else {
+	printf("Found %ld bytes at 0x%08lx\n", m->size, (u_long)&m->data);
+	puts(">>>>>>>>>>>>>>>>>>>>");
+	fflush(stdout);
+	write(1, &m->data, m->size);
+	fflush(stdout);
+	puts("<<<<<<<<<<<<<<<<<<<<");
+    }
+    return(0);
+}