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, 151 insertions, 0 deletions

diff --git a/arch/powerpc/boot/mktree.c b/arch/powerpc/boot/mktree.c
new file mode 100644
index 000000000..dc603f3c1
--- /dev/null
+++ b/arch/powerpc/boot/mktree.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Makes a tree bootable image for IBM Evaluation boards.
+ * Basically, just take a zImage, skip the ELF header, and stuff
+ * a 32 byte header on the front.
+ *
+ * We use htonl, which is a network macro, to make sure we're doing
+ * The Right Thing on an LE machine.  It's non-obvious, but it should
+ * work on anything BSD'ish.
+ */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <netinet/in.h>
+#ifdef __sun__
+#include <inttypes.h>
+#else
+#include <stdint.h>
+#endif
+
+/* This gets tacked on the front of the image.  There are also a few
+ * bytes allocated after the _start label used by the boot rom (see
+ * head.S for details).
+ */
+typedef struct boot_block {
+	uint32_t bb_magic;		/* 0x0052504F */
+	uint32_t bb_dest;		/* Target address of the image */
+	uint32_t bb_num_512blocks;	/* Size, rounded-up, in 512 byte blks */
+	uint32_t bb_debug_flag;	/* Run debugger or image after load */
+	uint32_t bb_entry_point;	/* The image address to start */
+	uint32_t bb_checksum;	/* 32 bit checksum including header */
+	uint32_t reserved[2];
+} boot_block_t;
+
+#define IMGBLK	512
+unsigned int	tmpbuf[IMGBLK / sizeof(unsigned int)];
+
+int main(int argc, char *argv[])
+{
+	int	in_fd, out_fd;
+	int	nblks, i;
+	unsigned int	cksum, *cp;
+	struct	stat	st;
+	boot_block_t	bt;
+
+	if (argc < 5) {
+		fprintf(stderr, "usage: %s <zImage-file> <boot-image> <load address> <entry point>\n",argv[0]);
+		exit(1);
+	}
+
+	if (stat(argv[1], &st) < 0) {
+		perror("stat");
+		exit(2);
+	}
+
+	nblks = (st.st_size + IMGBLK) / IMGBLK;
+
+	bt.bb_magic = htonl(0x0052504F);
+
+	/* If we have the optional entry point parameter, use it */
+	bt.bb_dest = htonl(strtoul(argv[3], NULL, 0));
+	bt.bb_entry_point = htonl(strtoul(argv[4], NULL, 0));
+
+	/* We know these from the linker command.
+	 * ...and then move it up into memory a little more so the
+	 * relocation can happen.
+	 */
+	bt.bb_num_512blocks = htonl(nblks);
+	bt.bb_debug_flag = 0;
+
+	bt.bb_checksum = 0;
+
+	/* To be neat and tidy :-).
+	*/
+	bt.reserved[0] = 0;
+	bt.reserved[1] = 0;
+
+	if ((in_fd = open(argv[1], O_RDONLY)) < 0) {
+		perror("zImage open");
+		exit(3);
+	}
+
+	if ((out_fd = open(argv[2], (O_RDWR | O_CREAT | O_TRUNC), 0666)) < 0) {
+		perror("bootfile open");
+		exit(3);
+	}
+
+	cksum = 0;
+	cp = (void *)&bt;
+	for (i = 0; i < sizeof(bt) / sizeof(unsigned int); i++)
+		cksum += *cp++;
+
+	/* Assume zImage is an ELF file, and skip the 64K header.
+	*/
+	if (read(in_fd, tmpbuf, sizeof(tmpbuf)) != sizeof(tmpbuf)) {
+		fprintf(stderr, "%s is too small to be an ELF image\n",
+				argv[1]);
+		exit(4);
+	}
+
+	if (tmpbuf[0] != htonl(0x7f454c46)) {
+		fprintf(stderr, "%s is not an ELF image\n", argv[1]);
+		exit(4);
+	}
+
+	if (lseek(in_fd, (64 * 1024), SEEK_SET) < 0) {
+		fprintf(stderr, "%s failed to seek in ELF image\n", argv[1]);
+		exit(4);
+	}
+
+	nblks -= (64 * 1024) / IMGBLK;
+
+	/* And away we go......
+	*/
+	if (write(out_fd, &bt, sizeof(bt)) != sizeof(bt)) {
+		perror("boot-image write");
+		exit(5);
+	}
+
+	while (nblks-- > 0) {
+		if (read(in_fd, tmpbuf, sizeof(tmpbuf)) < 0) {
+			perror("zImage read");
+			exit(5);
+		}
+		cp = tmpbuf;
+		for (i = 0; i < sizeof(tmpbuf) / sizeof(unsigned int); i++)
+			cksum += *cp++;
+		if (write(out_fd, tmpbuf, sizeof(tmpbuf)) != sizeof(tmpbuf)) {
+			perror("boot-image write");
+			exit(5);
+		}
+	}
+
+	/* rewrite the header with the computed checksum.
+	*/
+	bt.bb_checksum = htonl(cksum);
+	if (lseek(out_fd, 0, SEEK_SET) < 0) {
+		perror("rewrite seek");
+		exit(1);
+	}
+	if (write(out_fd, &bt, sizeof(bt)) != sizeof(bt)) {
+		perror("boot-image rewrite");
+		exit(1);
+	}
+
+	exit(0);
+}