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, 176 insertions, 0 deletions

diff --git a/arch/x86/boot/edd.c b/arch/x86/boot/edd.c
new file mode 100644
index 000000000..9956c6115
--- /dev/null
+++ b/arch/x86/boot/edd.c
@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *   Copyright 2009 Intel Corporation; author H. Peter Anvin
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Get EDD BIOS disk information
+ */
+
+#include "boot.h"
+#include <linux/edd.h>
+#include "string.h"
+
+#if IS_ENABLED(CONFIG_EDD)
+
+/*
+ * Read the MBR (first sector) from a specific device.
+ */
+static int read_mbr(u8 devno, void *buf)
+{
+	struct biosregs ireg, oreg;
+
+	initregs(&ireg);
+	ireg.ax = 0x0201;		/* Legacy Read, one sector */
+	ireg.cx = 0x0001;		/* Sector 0-0-1 */
+	ireg.dl = devno;
+	ireg.bx = (size_t)buf;
+
+	intcall(0x13, &ireg, &oreg);
+
+	return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
+}
+
+static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
+{
+	int sector_size;
+	char *mbrbuf_ptr, *mbrbuf_end;
+	u32 buf_base, mbr_base;
+	extern char _end[];
+	u16 mbr_magic;
+
+	sector_size = ei->params.bytes_per_sector;
+	if (!sector_size)
+		sector_size = 512; /* Best available guess */
+
+	/* Produce a naturally aligned buffer on the heap */
+	buf_base = (ds() << 4) + (u32)&_end;
+	mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
+	mbrbuf_ptr = _end + (mbr_base-buf_base);
+	mbrbuf_end = mbrbuf_ptr + sector_size;
+
+	/* Make sure we actually have space on the heap... */
+	if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
+		return -1;
+	if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
+		return -1;
+
+	memset(mbrbuf_ptr, 0, sector_size);
+	if (read_mbr(devno, mbrbuf_ptr))
+		return -1;
+
+	*mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
+	mbr_magic = *(u16 *)&mbrbuf_ptr[510];
+
+	/* check for valid MBR magic */
+	return mbr_magic == 0xAA55 ? 0 : -1;
+}
+
+static int get_edd_info(u8 devno, struct edd_info *ei)
+{
+	struct biosregs ireg, oreg;
+
+	memset(ei, 0, sizeof(*ei));
+
+	/* Check Extensions Present */
+
+	initregs(&ireg);
+	ireg.ah = 0x41;
+	ireg.bx = EDDMAGIC1;
+	ireg.dl = devno;
+	intcall(0x13, &ireg, &oreg);
+
+	if (oreg.eflags & X86_EFLAGS_CF)
+		return -1;	/* No extended information */
+
+	if (oreg.bx != EDDMAGIC2)
+		return -1;
+
+	ei->device  = devno;
+	ei->version = oreg.ah;		 /* EDD version number */
+	ei->interface_support = oreg.cx; /* EDD functionality subsets */
+
+	/* Extended Get Device Parameters */
+
+	ei->params.length = sizeof(ei->params);
+	ireg.ah = 0x48;
+	ireg.si = (size_t)&ei->params;
+	intcall(0x13, &ireg, &oreg);
+
+	/* Get legacy CHS parameters */
+
+	/* Ralf Brown recommends setting ES:DI to 0:0 */
+	ireg.ah = 0x08;
+	ireg.es = 0;
+	intcall(0x13, &ireg, &oreg);
+
+	if (!(oreg.eflags & X86_EFLAGS_CF)) {
+		ei->legacy_max_cylinder = oreg.ch + ((oreg.cl & 0xc0) << 2);
+		ei->legacy_max_head = oreg.dh;
+		ei->legacy_sectors_per_track = oreg.cl & 0x3f;
+	}
+
+	return 0;
+}
+
+void query_edd(void)
+{
+	char eddarg[8];
+	bool do_mbr = true;
+	bool do_edd = !IS_ENABLED(CONFIG_EDD_OFF);
+	bool be_quiet;
+	int devno;
+	struct edd_info ei, *edp;
+	u32 *mbrptr;
+
+	if (cmdline_find_option("edd", eddarg, sizeof(eddarg)) > 0) {
+		if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
+			do_edd = true;
+			do_mbr = false;
+		}
+		else if (!strcmp(eddarg, "off"))
+			do_edd = false;
+		else if (!strcmp(eddarg, "on"))
+			do_edd = true;
+	}
+
+	be_quiet = cmdline_find_option_bool("quiet");
+
+	edp    = boot_params.eddbuf;
+	mbrptr = boot_params.edd_mbr_sig_buffer;
+
+	if (!do_edd)
+		return;
+
+	/* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
+	 * so give a hint if this happens.
+	 */
+
+	if (!be_quiet)
+		printf("Probing EDD (edd=off to disable)... ");
+
+	for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
+		/*
+		 * Scan the BIOS-supported hard disks and query EDD
+		 * information...
+		 */
+		if (!get_edd_info(devno, &ei)
+		    && boot_params.eddbuf_entries < EDDMAXNR) {
+			memcpy(edp, &ei, sizeof(ei));
+			edp++;
+			boot_params.eddbuf_entries++;
+		}
+
+		if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
+			boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
+	}
+
+	if (!be_quiet)
+		printf("ok\n");
+}
+
+#endif