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, 187 insertions, 0 deletions

diff --git a/drivers/mtd/devices/mtdram.c b/drivers/mtd/devices/mtdram.c
new file mode 100644
index 000000000..3fff3cdd9
--- /dev/null
+++ b/drivers/mtd/devices/mtdram.c
@@ -0,0 +1,187 @@
+/*
+ * mtdram - a test mtd device
+ * Author: Alexander Larsson <alex@cendio.se>
+ *
+ * Copyright (c) 1999 Alexander Larsson <alex@cendio.se>
+ * Copyright (c) 2005 Joern Engel <joern@wh.fh-wedel.de>
+ *
+ * This code is GPL
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/ioport.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/mtdram.h>
+
+static unsigned long total_size = CONFIG_MTDRAM_TOTAL_SIZE;
+static unsigned long erase_size = CONFIG_MTDRAM_ERASE_SIZE;
+static unsigned long writebuf_size = 64;
+#define MTDRAM_TOTAL_SIZE (total_size * 1024)
+#define MTDRAM_ERASE_SIZE (erase_size * 1024)
+
+module_param(total_size, ulong, 0);
+MODULE_PARM_DESC(total_size, "Total device size in KiB");
+module_param(erase_size, ulong, 0);
+MODULE_PARM_DESC(erase_size, "Device erase block size in KiB");
+module_param(writebuf_size, ulong, 0);
+MODULE_PARM_DESC(writebuf_size, "Device write buf size in Bytes (Default: 64)");
+
+// We could store these in the mtd structure, but we only support 1 device..
+static struct mtd_info *mtd_info;
+
+static int check_offs_len(struct mtd_info *mtd, loff_t ofs, uint64_t len)
+{
+	int ret = 0;
+
+	/* Start address must align on block boundary */
+	if (mtd_mod_by_eb(ofs, mtd)) {
+		pr_debug("%s: unaligned address\n", __func__);
+		ret = -EINVAL;
+	}
+
+	/* Length must align on block boundary */
+	if (mtd_mod_by_eb(len, mtd)) {
+		pr_debug("%s: length not block aligned\n", __func__);
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
+{
+	if (check_offs_len(mtd, instr->addr, instr->len))
+		return -EINVAL;
+	memset((char *)mtd->priv + instr->addr, 0xff, instr->len);
+
+	return 0;
+}
+
+static int ram_point(struct mtd_info *mtd, loff_t from, size_t len,
+		size_t *retlen, void **virt, resource_size_t *phys)
+{
+	*virt = mtd->priv + from;
+	*retlen = len;
+
+	if (phys) {
+		/* limit retlen to the number of contiguous physical pages */
+		unsigned long page_ofs = offset_in_page(*virt);
+		void *addr = *virt - page_ofs;
+		unsigned long pfn1, pfn0 = vmalloc_to_pfn(addr);
+
+		*phys = __pfn_to_phys(pfn0) + page_ofs;
+		len += page_ofs;
+		while (len > PAGE_SIZE) {
+			len -= PAGE_SIZE;
+			addr += PAGE_SIZE;
+			pfn0++;
+			pfn1 = vmalloc_to_pfn(addr);
+			if (pfn1 != pfn0) {
+				*retlen = addr - *virt;
+				break;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static int ram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
+{
+	return 0;
+}
+
+static int ram_read(struct mtd_info *mtd, loff_t from, size_t len,
+		size_t *retlen, u_char *buf)
+{
+	memcpy(buf, mtd->priv + from, len);
+	*retlen = len;
+	return 0;
+}
+
+static int ram_write(struct mtd_info *mtd, loff_t to, size_t len,
+		size_t *retlen, const u_char *buf)
+{
+	memcpy((char *)mtd->priv + to, buf, len);
+	*retlen = len;
+	return 0;
+}
+
+static void __exit cleanup_mtdram(void)
+{
+	if (mtd_info) {
+		mtd_device_unregister(mtd_info);
+		vfree(mtd_info->priv);
+		kfree(mtd_info);
+	}
+}
+
+int mtdram_init_device(struct mtd_info *mtd, void *mapped_address,
+		unsigned long size, const char *name)
+{
+	memset(mtd, 0, sizeof(*mtd));
+
+	/* Setup the MTD structure */
+	mtd->name = name;
+	mtd->type = MTD_RAM;
+	mtd->flags = MTD_CAP_RAM;
+	mtd->size = size;
+	mtd->writesize = 1;
+	mtd->writebufsize = writebuf_size;
+	mtd->erasesize = MTDRAM_ERASE_SIZE;
+	mtd->priv = mapped_address;
+
+	mtd->owner = THIS_MODULE;
+	mtd->_erase = ram_erase;
+	mtd->_point = ram_point;
+	mtd->_unpoint = ram_unpoint;
+	mtd->_read = ram_read;
+	mtd->_write = ram_write;
+
+	if (mtd_device_register(mtd, NULL, 0))
+		return -EIO;
+
+	return 0;
+}
+
+static int __init init_mtdram(void)
+{
+	void *addr;
+	int err;
+
+	if (!total_size)
+		return -EINVAL;
+
+	/* Allocate some memory */
+	mtd_info = kmalloc_obj(struct mtd_info);
+	if (!mtd_info)
+		return -ENOMEM;
+
+	addr = vmalloc(MTDRAM_TOTAL_SIZE);
+	if (!addr) {
+		kfree(mtd_info);
+		mtd_info = NULL;
+		return -ENOMEM;
+	}
+	err = mtdram_init_device(mtd_info, addr, MTDRAM_TOTAL_SIZE, "mtdram test device");
+	if (err) {
+		vfree(addr);
+		kfree(mtd_info);
+		mtd_info = NULL;
+		return err;
+	}
+	memset(mtd_info->priv, 0xff, MTDRAM_TOTAL_SIZE);
+	return err;
+}
+
+module_init(init_mtdram);
+module_exit(cleanup_mtdram);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Alexander Larsson <alexl@redhat.com>");
+MODULE_DESCRIPTION("Simulated MTD driver for testing");