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, 231 insertions, 0 deletions

diff --git a/drivers/mtd/maps/dc21285.c b/drivers/mtd/maps/dc21285.c
new file mode 100644
index 000000000..70a3db3ab
--- /dev/null
+++ b/drivers/mtd/maps/dc21285.c
@@ -0,0 +1,231 @@
+/*
+ * MTD map driver for flash on the DC21285 (the StrongARM-110 companion chip)
+ *
+ * (C) 2000  Nicolas Pitre <nico@fluxnic.net>
+ *
+ * This code is GPL
+ */
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/partitions.h>
+
+#include <asm/io.h>
+#include <asm/hardware/dec21285.h>
+#include <asm/mach-types.h>
+
+
+static struct mtd_info *dc21285_mtd;
+
+#ifdef CONFIG_ARCH_NETWINDER
+/*
+ * This is really ugly, but it seams to be the only
+ * realiable way to do it, as the cpld state machine
+ * is unpredictible. So we have a 25us penalty per
+ * write access.
+ */
+static void nw_en_write(void)
+{
+	unsigned long flags;
+
+	/*
+	 * we want to write a bit pattern XXX1 to Xilinx to enable
+	 * the write gate, which will be open for about the next 2ms.
+	 */
+	raw_spin_lock_irqsave(&nw_gpio_lock, flags);
+	nw_cpld_modify(CPLD_FLASH_WR_ENABLE, CPLD_FLASH_WR_ENABLE);
+	raw_spin_unlock_irqrestore(&nw_gpio_lock, flags);
+
+	/*
+	 * let the ISA bus to catch on...
+	 */
+	udelay(25);
+}
+#else
+#define nw_en_write() do { } while (0)
+#endif
+
+static map_word dc21285_read8(struct map_info *map, unsigned long ofs)
+{
+	map_word val;
+	val.x[0] = *(uint8_t*)(map->virt + ofs);
+	return val;
+}
+
+static map_word dc21285_read16(struct map_info *map, unsigned long ofs)
+{
+	map_word val;
+	val.x[0] = *(uint16_t*)(map->virt + ofs);
+	return val;
+}
+
+static map_word dc21285_read32(struct map_info *map, unsigned long ofs)
+{
+	map_word val;
+	val.x[0] = *(uint32_t*)(map->virt + ofs);
+	return val;
+}
+
+static void dc21285_copy_from(struct map_info *map, void *to, unsigned long from, ssize_t len)
+{
+	memcpy(to, (void*)(map->virt + from), len);
+}
+
+static void dc21285_write8(struct map_info *map, const map_word d, unsigned long adr)
+{
+	if (machine_is_netwinder())
+		nw_en_write();
+	*CSR_ROMWRITEREG = adr & 3;
+	adr &= ~3;
+	*(uint8_t*)(map->virt + adr) = d.x[0];
+}
+
+static void dc21285_write16(struct map_info *map, const map_word d, unsigned long adr)
+{
+	if (machine_is_netwinder())
+		nw_en_write();
+	*CSR_ROMWRITEREG = adr & 3;
+	adr &= ~3;
+	*(uint16_t*)(map->virt + adr) = d.x[0];
+}
+
+static void dc21285_write32(struct map_info *map, const map_word d, unsigned long adr)
+{
+	if (machine_is_netwinder())
+		nw_en_write();
+	*(uint32_t*)(map->virt + adr) = d.x[0];
+}
+
+static void dc21285_copy_to_32(struct map_info *map, unsigned long to, const void *from, ssize_t len)
+{
+	while (len > 0) {
+		map_word d;
+		d.x[0] = *((uint32_t*)from);
+		dc21285_write32(map, d, to);
+		from += 4;
+		to += 4;
+		len -= 4;
+	}
+}
+
+static void dc21285_copy_to_16(struct map_info *map, unsigned long to, const void *from, ssize_t len)
+{
+	while (len > 0) {
+		map_word d;
+		d.x[0] = *((uint16_t*)from);
+		dc21285_write16(map, d, to);
+		from += 2;
+		to += 2;
+		len -= 2;
+	}
+}
+
+static void dc21285_copy_to_8(struct map_info *map, unsigned long to, const void *from, ssize_t len)
+{
+	map_word d;
+	d.x[0] = *((uint8_t*)from);
+	dc21285_write8(map, d, to);
+	from++;
+	to++;
+	len--;
+}
+
+static struct map_info dc21285_map = {
+	.name = "DC21285 flash",
+	.phys = NO_XIP,
+	.size = 16*1024*1024,
+	.copy_from = dc21285_copy_from,
+};
+
+/* Partition stuff */
+static const char * const probes[] = { "RedBoot", "cmdlinepart", NULL };
+
+static int __init init_dc21285(void)
+{
+	/* Determine bankwidth */
+	switch (*CSR_SA110_CNTL & (3<<14)) {
+		case SA110_CNTL_ROMWIDTH_8:
+			dc21285_map.bankwidth = 1;
+			dc21285_map.read = dc21285_read8;
+			dc21285_map.write = dc21285_write8;
+			dc21285_map.copy_to = dc21285_copy_to_8;
+			break;
+		case SA110_CNTL_ROMWIDTH_16:
+			dc21285_map.bankwidth = 2;
+			dc21285_map.read = dc21285_read16;
+			dc21285_map.write = dc21285_write16;
+			dc21285_map.copy_to = dc21285_copy_to_16;
+			break;
+		case SA110_CNTL_ROMWIDTH_32:
+			dc21285_map.bankwidth = 4;
+			dc21285_map.read = dc21285_read32;
+			dc21285_map.write = dc21285_write32;
+			dc21285_map.copy_to = dc21285_copy_to_32;
+			break;
+		default:
+			printk (KERN_ERR "DC21285 flash: undefined bankwidth\n");
+			return -ENXIO;
+	}
+	printk (KERN_NOTICE "DC21285 flash support (%d-bit bankwidth)\n",
+		dc21285_map.bankwidth*8);
+
+	/* Let's map the flash area */
+	dc21285_map.virt = ioremap(DC21285_FLASH, 16*1024*1024);
+	if (!dc21285_map.virt) {
+		printk("Failed to ioremap\n");
+		return -EIO;
+	}
+
+	if (machine_is_ebsa285()) {
+		dc21285_mtd = do_map_probe("cfi_probe", &dc21285_map);
+	} else {
+		dc21285_mtd = do_map_probe("jedec_probe", &dc21285_map);
+	}
+
+	if (!dc21285_mtd) {
+		iounmap(dc21285_map.virt);
+		return -ENXIO;
+	}
+
+	dc21285_mtd->owner = THIS_MODULE;
+
+	mtd_device_parse_register(dc21285_mtd, probes, NULL, NULL, 0);
+
+	if(machine_is_ebsa285()) {
+		/*
+		 * Flash timing is determined with bits 19-16 of the
+		 * CSR_SA110_CNTL.  The value is the number of wait cycles, or
+		 * 0 for 16 cycles (the default).  Cycles are 20 ns.
+		 * Here we use 7 for 140 ns flash chips.
+		 */
+		/* access time */
+		*CSR_SA110_CNTL = ((*CSR_SA110_CNTL & ~0x000f0000) | (7 << 16));
+		/* burst time */
+		*CSR_SA110_CNTL = ((*CSR_SA110_CNTL & ~0x00f00000) | (7 << 20));
+		/* tristate time */
+		*CSR_SA110_CNTL = ((*CSR_SA110_CNTL & ~0x0f000000) | (7 << 24));
+	}
+
+	return 0;
+}
+
+static void __exit cleanup_dc21285(void)
+{
+	mtd_device_unregister(dc21285_mtd);
+	map_destroy(dc21285_mtd);
+	iounmap(dc21285_map.virt);
+}
+
+module_init(init_dc21285);
+module_exit(cleanup_dc21285);
+
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Nicolas Pitre <nico@fluxnic.net>");
+MODULE_DESCRIPTION("MTD map driver for DC21285 boards");