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, 179 insertions, 0 deletions

diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c
new file mode 100644
index 000000000..4e382d95e
--- /dev/null
+++ b/arch/x86/boot/main.c
@@ -0,0 +1,179 @@
+// 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
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Main module for the real-mode kernel code
+ */
+#include <linux/build_bug.h>
+
+#include "boot.h"
+#include "string.h"
+
+struct boot_params boot_params __attribute__((aligned(16)));
+
+struct port_io_ops pio_ops;
+
+char *HEAP = _end;
+char *heap_end = _end;		/* Default end of heap = no heap */
+
+/*
+ * Copy the header into the boot parameter block.  Since this
+ * screws up the old-style command line protocol, adjust by
+ * filling in the new-style command line pointer instead.
+ */
+static void copy_boot_params(void)
+{
+	struct old_cmdline {
+		u16 cl_magic;
+		u16 cl_offset;
+	};
+	const struct old_cmdline * const oldcmd = absolute_pointer(OLD_CL_ADDRESS);
+
+	BUILD_BUG_ON(sizeof(boot_params) != 4096);
+	memcpy(&boot_params.hdr, &hdr, sizeof(hdr));
+
+	if (!boot_params.hdr.cmd_line_ptr && oldcmd->cl_magic == OLD_CL_MAGIC) {
+		/* Old-style command line protocol */
+		u16 cmdline_seg;
+
+		/*
+		 * Figure out if the command line falls in the region
+		 * of memory that an old kernel would have copied up
+		 * to 0x90000...
+		 */
+		if (oldcmd->cl_offset < boot_params.hdr.setup_move_size)
+			cmdline_seg = ds();
+		else
+			cmdline_seg = 0x9000;
+
+		boot_params.hdr.cmd_line_ptr = (cmdline_seg << 4) + oldcmd->cl_offset;
+	}
+}
+
+/*
+ * Query the keyboard lock status as given by the BIOS, and
+ * set the keyboard repeat rate to maximum.  Unclear why the latter
+ * is done here; this might be possible to kill off as stale code.
+ */
+static void keyboard_init(void)
+{
+	struct biosregs ireg, oreg;
+
+	initregs(&ireg);
+
+	ireg.ah = 0x02;		/* Get keyboard status */
+	intcall(0x16, &ireg, &oreg);
+	boot_params.kbd_status = oreg.al;
+
+	ireg.ax = 0x0305;	/* Set keyboard repeat rate */
+	intcall(0x16, &ireg, NULL);
+}
+
+/*
+ * Get Intel SpeedStep (IST) information.
+ */
+static void query_ist(void)
+{
+	struct biosregs ireg, oreg;
+
+	/*
+	 * Some older BIOSes apparently crash on this call, so filter
+	 * it from machines too old to have SpeedStep at all.
+	 */
+	if (cpu.level < 6)
+		return;
+
+	initregs(&ireg);
+	ireg.ax  = 0xe980;	 /* IST Support */
+	ireg.edx = 0x47534943;	 /* Request value */
+	intcall(0x15, &ireg, &oreg);
+
+	boot_params.ist_info.signature  = oreg.eax;
+	boot_params.ist_info.command    = oreg.ebx;
+	boot_params.ist_info.event      = oreg.ecx;
+	boot_params.ist_info.perf_level = oreg.edx;
+}
+
+/*
+ * Tell the BIOS what CPU mode we intend to run in.
+ */
+static void set_bios_mode(void)
+{
+#ifdef CONFIG_X86_64
+	struct biosregs ireg;
+
+	initregs(&ireg);
+	ireg.ax = 0xec00;
+	ireg.bx = 2;
+	intcall(0x15, &ireg, NULL);
+#endif
+}
+
+static void init_heap(void)
+{
+	char *stack_end;
+
+	if (boot_params.hdr.loadflags & CAN_USE_HEAP) {
+		stack_end = (char *) (current_stack_pointer - STACK_SIZE);
+		heap_end = (char *) ((size_t)boot_params.hdr.heap_end_ptr + 0x200);
+		if (heap_end > stack_end)
+			heap_end = stack_end;
+	} else {
+		/* Boot protocol 2.00 only, no heap available */
+		puts("WARNING: Ancient bootloader, some functionality may be limited!\n");
+	}
+}
+
+void main(void)
+{
+	init_default_io_ops();
+
+	/* First, copy the boot header into the "zeropage" */
+	copy_boot_params();
+
+	/* Initialize the early-boot console */
+	console_init();
+	if (cmdline_find_option_bool("debug"))
+		puts("early console in setup code\n");
+
+	/* End of heap check */
+	init_heap();
+
+	/* Make sure we have all the proper CPU support */
+	if (validate_cpu()) {
+		puts("Unable to boot - please use a kernel appropriate for your CPU.\n");
+		die();
+	}
+
+	/* Tell the BIOS what CPU mode we intend to run in */
+	set_bios_mode();
+
+	/* Detect memory layout */
+	detect_memory();
+
+	/* Set keyboard repeat rate (why?) and query the lock flags */
+	keyboard_init();
+
+	/* Query Intel SpeedStep (IST) information */
+	query_ist();
+
+	/* Query APM information */
+	if (IS_ENABLED(CONFIG_APM))
+		query_apm_bios();
+
+	/* Query EDD information */
+	if (IS_ENABLED(CONFIG_EDD))
+		query_edd();
+
+	/* Set the video mode */
+	set_video();
+
+	/* Do the last things and invoke protected mode */
+	go_to_protected_mode();
+}