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, 156 insertions, 0 deletions

diff --git a/arch/x86/boot/cmdline.c b/arch/x86/boot/cmdline.c
new file mode 100644
index 000000000..21d56ae83
--- /dev/null
+++ b/arch/x86/boot/cmdline.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Simple command-line parser for early boot.
+ */
+
+#include "boot.h"
+
+static inline int myisspace(u8 c)
+{
+	return c <= ' ';	/* Close enough approximation */
+}
+
+/*
+ * Find a non-boolean option, that is, "option=argument".  In accordance
+ * with standard Linux practice, if this option is repeated, this returns
+ * the last instance on the command line.
+ *
+ * Returns the length of the argument (regardless of if it was
+ * truncated to fit in the buffer), or -1 on not found.
+ */
+int __cmdline_find_option(unsigned long cmdline_ptr, const char *option, char *buffer, int bufsize)
+{
+	addr_t cptr;
+	char c;
+	int len = -1;
+	const char *opptr = NULL;
+	char *bufptr = buffer;
+	enum {
+		st_wordstart,	/* Start of word/after whitespace */
+		st_wordcmp,	/* Comparing this word */
+		st_wordskip,	/* Miscompare, skip */
+		st_bufcpy	/* Copying this to buffer */
+	} state = st_wordstart;
+
+	if (!cmdline_ptr)
+		return -1;      /* No command line */
+
+	cptr = cmdline_ptr & 0xf;
+	set_fs(cmdline_ptr >> 4);
+
+	while (cptr < 0x10000 && (c = rdfs8(cptr++))) {
+		switch (state) {
+		case st_wordstart:
+			if (myisspace(c))
+				break;
+
+			/* else */
+			state = st_wordcmp;
+			opptr = option;
+			fallthrough;
+
+		case st_wordcmp:
+			if (c == '=' && !*opptr) {
+				len = 0;
+				bufptr = buffer;
+				state = st_bufcpy;
+			} else if (myisspace(c)) {
+				state = st_wordstart;
+			} else if (c != *opptr++) {
+				state = st_wordskip;
+			}
+			break;
+
+		case st_wordskip:
+			if (myisspace(c))
+				state = st_wordstart;
+			break;
+
+		case st_bufcpy:
+			if (myisspace(c)) {
+				state = st_wordstart;
+			} else {
+				if (len < bufsize-1)
+					*bufptr++ = c;
+				len++;
+			}
+			break;
+		}
+	}
+
+	if (bufsize)
+		*bufptr = '\0';
+
+	return len;
+}
+
+/*
+ * Find a boolean option (like quiet,noapic,nosmp....)
+ *
+ * Returns the position of that option (starts counting with 1)
+ * or 0 on not found
+ */
+int __cmdline_find_option_bool(unsigned long cmdline_ptr, const char *option)
+{
+	addr_t cptr;
+	char c;
+	int pos = 0, wstart = 0;
+	const char *opptr = NULL;
+	enum {
+		st_wordstart,	/* Start of word/after whitespace */
+		st_wordcmp,	/* Comparing this word */
+		st_wordskip,	/* Miscompare, skip */
+	} state = st_wordstart;
+
+	if (!cmdline_ptr)
+		return -1;      /* No command line */
+
+	cptr = cmdline_ptr & 0xf;
+	set_fs(cmdline_ptr >> 4);
+
+	while (cptr < 0x10000) {
+		c = rdfs8(cptr++);
+		pos++;
+
+		switch (state) {
+		case st_wordstart:
+			if (!c)
+				return 0;
+			else if (myisspace(c))
+				break;
+
+			state = st_wordcmp;
+			opptr = option;
+			wstart = pos;
+			fallthrough;
+
+		case st_wordcmp:
+			if (!*opptr)
+				if (!c || myisspace(c))
+					return wstart;
+				else
+					state = st_wordskip;
+			else if (!c)
+				return 0;
+			else if (c != *opptr++)
+				state = st_wordskip;
+			break;
+
+		case st_wordskip:
+			if (!c)
+				return 0;
+			else if (myisspace(c))
+				state = st_wordstart;
+			break;
+		}
+	}
+
+	return 0;	/* Buffer overrun */
+}