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, 158 insertions, 0 deletions

diff --git a/io_uring/filetable.c b/io_uring/filetable.c
new file mode 100644
index 000000000..cb1838c9f
--- /dev/null
+++ b/io_uring/filetable.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/nospec.h>
+#include <linux/io_uring.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "io_uring.h"
+#include "rsrc.h"
+#include "filetable.h"
+
+static int io_file_bitmap_get(struct io_ring_ctx *ctx)
+{
+	struct io_file_table *table = &ctx->file_table;
+	unsigned long nr = ctx->file_alloc_end;
+	int ret;
+
+	if (!table->bitmap)
+		return -ENFILE;
+
+	if (table->alloc_hint < ctx->file_alloc_start ||
+	    table->alloc_hint >= ctx->file_alloc_end)
+		table->alloc_hint = ctx->file_alloc_start;
+
+	do {
+		ret = find_next_zero_bit(table->bitmap, nr, table->alloc_hint);
+		if (ret != nr)
+			return ret;
+
+		if (table->alloc_hint == ctx->file_alloc_start)
+			break;
+		nr = table->alloc_hint;
+		table->alloc_hint = ctx->file_alloc_start;
+	} while (1);
+
+	return -ENFILE;
+}
+
+bool io_alloc_file_tables(struct io_ring_ctx *ctx, struct io_file_table *table,
+			  unsigned nr_files)
+{
+	if (io_rsrc_data_alloc(&table->data, nr_files))
+		return false;
+	table->bitmap = bitmap_zalloc(nr_files, GFP_KERNEL_ACCOUNT);
+	if (table->bitmap)
+		return true;
+	io_rsrc_data_free(ctx, &table->data);
+	return false;
+}
+
+void io_free_file_tables(struct io_ring_ctx *ctx, struct io_file_table *table)
+{
+	io_rsrc_data_free(ctx, &table->data);
+	bitmap_free(table->bitmap);
+	table->bitmap = NULL;
+}
+
+static int io_install_fixed_file(struct io_ring_ctx *ctx, struct file *file,
+				 u32 slot_index)
+	__must_hold(&ctx->uring_lock)
+{
+	struct io_rsrc_node *node;
+
+	if (io_is_uring_fops(file))
+		return -EBADF;
+	if (!ctx->file_table.data.nr)
+		return -ENXIO;
+	if (slot_index >= ctx->file_table.data.nr)
+		return -EINVAL;
+
+	node = io_rsrc_node_alloc(ctx, IORING_RSRC_FILE);
+	if (!node)
+		return -ENOMEM;
+
+	if (!io_reset_rsrc_node(ctx, &ctx->file_table.data, slot_index))
+		io_file_bitmap_set(&ctx->file_table, slot_index);
+
+	ctx->file_table.data.nodes[slot_index] = node;
+	io_fixed_file_set(node, file);
+	return 0;
+}
+
+int __io_fixed_fd_install(struct io_ring_ctx *ctx, struct file *file,
+			  unsigned int file_slot)
+{
+	bool alloc_slot = file_slot == IORING_FILE_INDEX_ALLOC;
+	int ret;
+
+	if (alloc_slot) {
+		ret = io_file_bitmap_get(ctx);
+		if (unlikely(ret < 0))
+			return ret;
+		file_slot = ret;
+	} else {
+		file_slot--;
+	}
+
+	ret = io_install_fixed_file(ctx, file, file_slot);
+	if (!ret && alloc_slot)
+		ret = file_slot;
+	return ret;
+}
+/*
+ * Note when io_fixed_fd_install() returns error value, it will ensure
+ * fput() is called correspondingly.
+ */
+int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
+			struct file *file, unsigned int file_slot)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	int ret;
+
+	io_ring_submit_lock(ctx, issue_flags);
+	ret = __io_fixed_fd_install(ctx, file, file_slot);
+	io_ring_submit_unlock(ctx, issue_flags);
+
+	if (unlikely(ret < 0))
+		fput(file);
+	return ret;
+}
+
+int io_fixed_fd_remove(struct io_ring_ctx *ctx, unsigned int offset)
+{
+	struct io_rsrc_node *node;
+
+	if (unlikely(!ctx->file_table.data.nr))
+		return -ENXIO;
+	if (offset >= ctx->file_table.data.nr)
+		return -EINVAL;
+
+	node = io_rsrc_node_lookup(&ctx->file_table.data, offset);
+	if (!node)
+		return -EBADF;
+	io_reset_rsrc_node(ctx, &ctx->file_table.data, offset);
+	io_file_bitmap_clear(&ctx->file_table, offset);
+	return 0;
+}
+
+int io_register_file_alloc_range(struct io_ring_ctx *ctx,
+				 struct io_uring_file_index_range __user *arg)
+{
+	struct io_uring_file_index_range range;
+	u32 end;
+
+	if (copy_from_user(&range, arg, sizeof(range)))
+		return -EFAULT;
+	if (check_add_overflow(range.off, range.len, &end))
+		return -EOVERFLOW;
+	if (range.resv || end > ctx->file_table.data.nr)
+		return -EINVAL;
+
+	io_file_table_set_alloc_range(ctx, range.off, range.len);
+	return 0;
+}