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, 274 insertions, 0 deletions

diff --git a/arch/m68k/atari/nvram.c b/arch/m68k/atari/nvram.c
new file mode 100644
index 000000000..ededc3137
--- /dev/null
+++ b/arch/m68k/atari/nvram.c
@@ -0,0 +1,274 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * CMOS/NV-RAM driver for Atari. Adapted from drivers/char/nvram.c.
+ * Copyright (C) 1997 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
+ * idea by and with help from Richard Jelinek <rj@suse.de>
+ * Portions copyright (c) 2001,2002 Sun Microsystems (thockin@sun.com)
+ * Further contributions from Cesar Barros, Erik Gilling, Tim Hockin and
+ * Wim Van Sebroeck.
+ */
+
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/mc146818rtc.h>
+#include <linux/module.h>
+#include <linux/nvram.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/spinlock.h>
+#include <linux/string_choices.h>
+#include <linux/types.h>
+
+#include <asm/atarihw.h>
+#include <asm/atariints.h>
+
+#define NVRAM_BYTES		50
+
+/* It is worth noting that these functions all access bytes of general
+ * purpose memory in the NVRAM - that is to say, they all add the
+ * NVRAM_FIRST_BYTE offset. Pass them offsets into NVRAM as if you did not
+ * know about the RTC cruft.
+ */
+
+/* Note that *all* calls to CMOS_READ and CMOS_WRITE must be done with
+ * rtc_lock held. Due to the index-port/data-port design of the RTC, we
+ * don't want two different things trying to get to it at once. (e.g. the
+ * periodic 11 min sync from kernel/time/ntp.c vs. this driver.)
+ */
+
+static unsigned char __nvram_read_byte(int i)
+{
+	return CMOS_READ(NVRAM_FIRST_BYTE + i);
+}
+
+/* This races nicely with trying to read with checksum checking */
+static void __nvram_write_byte(unsigned char c, int i)
+{
+	CMOS_WRITE(c, NVRAM_FIRST_BYTE + i);
+}
+
+/* On Ataris, the checksum is over all bytes except the checksum bytes
+ * themselves; these are at the very end.
+ */
+#define ATARI_CKS_RANGE_START	0
+#define ATARI_CKS_RANGE_END	47
+#define ATARI_CKS_LOC		48
+
+static int __nvram_check_checksum(void)
+{
+	int i;
+	unsigned char sum = 0;
+
+	for (i = ATARI_CKS_RANGE_START; i <= ATARI_CKS_RANGE_END; ++i)
+		sum += __nvram_read_byte(i);
+	return (__nvram_read_byte(ATARI_CKS_LOC) == (~sum & 0xff)) &&
+	       (__nvram_read_byte(ATARI_CKS_LOC + 1) == (sum & 0xff));
+}
+
+static void __nvram_set_checksum(void)
+{
+	int i;
+	unsigned char sum = 0;
+
+	for (i = ATARI_CKS_RANGE_START; i <= ATARI_CKS_RANGE_END; ++i)
+		sum += __nvram_read_byte(i);
+	__nvram_write_byte(~sum, ATARI_CKS_LOC);
+	__nvram_write_byte(sum, ATARI_CKS_LOC + 1);
+}
+
+long atari_nvram_set_checksum(void)
+{
+	spin_lock_irq(&rtc_lock);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+	return 0;
+}
+
+long atari_nvram_initialize(void)
+{
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	for (i = 0; i < NVRAM_BYTES; ++i)
+		__nvram_write_byte(0, i);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+	return 0;
+}
+
+ssize_t atari_nvram_read(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		*p = __nvram_read_byte(i);
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+ssize_t atari_nvram_write(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		__nvram_write_byte(*p, i);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+ssize_t atari_nvram_get_size(void)
+{
+	return NVRAM_BYTES;
+}
+
+#ifdef CONFIG_PROC_FS
+static struct {
+	unsigned char val;
+	const char *name;
+} boot_prefs[] = {
+	{ 0x80, "TOS" },
+	{ 0x40, "ASV" },
+	{ 0x20, "NetBSD (?)" },
+	{ 0x10, "Linux" },
+	{ 0x00, "unspecified" },
+};
+
+static const char * const languages[] = {
+	"English (US)",
+	"German",
+	"French",
+	"English (UK)",
+	"Spanish",
+	"Italian",
+	"6 (undefined)",
+	"Swiss (French)",
+	"Swiss (German)",
+};
+
+static const char * const dateformat[] = {
+	"MM%cDD%cYY",
+	"DD%cMM%cYY",
+	"YY%cMM%cDD",
+	"YY%cDD%cMM",
+	"4 (undefined)",
+	"5 (undefined)",
+	"6 (undefined)",
+	"7 (undefined)",
+};
+
+static const char * const colors[] = {
+	"2", "4", "16", "256", "65536", "??", "??", "??"
+};
+
+static void atari_nvram_proc_read(unsigned char *nvram, struct seq_file *seq,
+				  void *offset)
+{
+	int checksum;
+	int i;
+	unsigned int vmode;
+
+	spin_lock_irq(&rtc_lock);
+	checksum = __nvram_check_checksum();
+	spin_unlock_irq(&rtc_lock);
+
+	seq_printf(seq, "Checksum status  : %svalid\n", checksum ? "" : "not ");
+
+	seq_puts(seq, "Boot preference  : ");
+	for (i = ARRAY_SIZE(boot_prefs) - 1; i >= 0; --i)
+		if (nvram[1] == boot_prefs[i].val) {
+			seq_printf(seq, "%s\n", boot_prefs[i].name);
+			break;
+		}
+	if (i < 0)
+		seq_printf(seq, "0x%02x (undefined)\n", nvram[1]);
+
+	seq_printf(seq, "SCSI arbitration : %s\n",
+		   str_on_off(nvram[16] & 0x80));
+	seq_puts(seq, "SCSI host ID     : ");
+	if (nvram[16] & 0x80)
+		seq_printf(seq, "%d\n", nvram[16] & 7);
+	else
+		seq_puts(seq, "n/a\n");
+
+	if (!MACH_IS_FALCON)
+		return;
+
+	seq_puts(seq, "OS language      : ");
+	if (nvram[6] < ARRAY_SIZE(languages))
+		seq_printf(seq, "%s\n", languages[nvram[6]]);
+	else
+		seq_printf(seq, "%u (undefined)\n", nvram[6]);
+	seq_puts(seq, "Keyboard language: ");
+	if (nvram[7] < ARRAY_SIZE(languages))
+		seq_printf(seq, "%s\n", languages[nvram[7]]);
+	else
+		seq_printf(seq, "%u (undefined)\n", nvram[7]);
+	seq_puts(seq, "Date format      : ");
+	seq_printf(seq, dateformat[nvram[8] & 7],
+		   nvram[9] ? nvram[9] : '/', nvram[9] ? nvram[9] : '/');
+	seq_printf(seq, ", %dh clock\n", nvram[8] & 16 ? 24 : 12);
+	seq_puts(seq, "Boot delay       : ");
+	if (nvram[10] == 0)
+		seq_puts(seq, "default\n");
+	else
+		seq_printf(seq, "%ds%s\n", nvram[10],
+			   nvram[10] < 8 ? ", no memory test" : "");
+
+	vmode = (nvram[14] << 8) | nvram[15];
+	seq_printf(seq,
+		   "Video mode       : %s colors, %d columns, %s %s monitor\n",
+		   colors[vmode & 7], vmode & 8 ? 80 : 40,
+		   vmode & 16 ? "VGA" : "TV", vmode & 32 ? "PAL" : "NTSC");
+	seq_printf(seq,
+		   "                   %soverscan, compat. mode %s%s\n",
+		   vmode & 64 ? "" : "no ", str_on_off(vmode & 128),
+		   vmode & 256 ?
+		   (vmode & 16 ? ", line doubling" : ", half screen") : "");
+}
+
+static int nvram_proc_read(struct seq_file *seq, void *offset)
+{
+	unsigned char contents[NVRAM_BYTES];
+	int i;
+
+	spin_lock_irq(&rtc_lock);
+	for (i = 0; i < NVRAM_BYTES; ++i)
+		contents[i] = __nvram_read_byte(i);
+	spin_unlock_irq(&rtc_lock);
+
+	atari_nvram_proc_read(contents, seq, offset);
+
+	return 0;
+}
+
+static int __init atari_nvram_init(void)
+{
+	if (!(MACH_IS_ATARI && ATARIHW_PRESENT(TT_CLK)))
+		return -ENODEV;
+
+	if (!proc_create_single("driver/nvram", 0, NULL, nvram_proc_read)) {
+		pr_err("nvram: can't create /proc/driver/nvram\n");
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+device_initcall(atari_nvram_init);
+#endif /* CONFIG_PROC_FS */