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, 154 insertions, 0 deletions

diff --git a/fs/squashfs/zstd_wrapper.c b/fs/squashfs/zstd_wrapper.c
new file mode 100644
index 000000000..487fbc51d
--- /dev/null
+++ b/fs/squashfs/zstd_wrapper.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Squashfs - a compressed read only filesystem for Linux
+ *
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * zstd_wrapper.c
+ */
+
+#include <linux/mutex.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/zstd.h>
+#include <linux/vmalloc.h>
+
+#include "squashfs_fs.h"
+#include "squashfs_fs_sb.h"
+#include "squashfs.h"
+#include "decompressor.h"
+#include "page_actor.h"
+
+struct workspace {
+	void *mem;
+	size_t mem_size;
+	size_t window_size;
+};
+
+static void *zstd_init(struct squashfs_sb_info *msblk, void *buff)
+{
+	struct workspace *wksp = kmalloc_obj(*wksp);
+
+	if (wksp == NULL)
+		goto failed;
+	wksp->window_size = max_t(size_t,
+			msblk->block_size, SQUASHFS_METADATA_SIZE);
+	wksp->mem_size = zstd_dstream_workspace_bound(wksp->window_size);
+	wksp->mem = vmalloc(wksp->mem_size);
+	if (wksp->mem == NULL)
+		goto failed;
+
+	return wksp;
+
+failed:
+	ERROR("Failed to allocate zstd workspace\n");
+	kfree(wksp);
+	return ERR_PTR(-ENOMEM);
+}
+
+
+static void zstd_free(void *strm)
+{
+	struct workspace *wksp = strm;
+
+	if (wksp)
+		vfree(wksp->mem);
+	kfree(wksp);
+}
+
+
+static int zstd_uncompress(struct squashfs_sb_info *msblk, void *strm,
+	struct bio *bio, int offset, int length,
+	struct squashfs_page_actor *output)
+{
+	struct workspace *wksp = strm;
+	zstd_dstream *stream;
+	size_t total_out = 0;
+	int error = 0;
+	zstd_in_buffer in_buf = { NULL, 0, 0 };
+	zstd_out_buffer out_buf = { NULL, 0, 0 };
+	struct bvec_iter_all iter_all = {};
+	struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
+
+	stream = zstd_init_dstream(wksp->window_size, wksp->mem, wksp->mem_size);
+
+	if (!stream) {
+		ERROR("Failed to initialize zstd decompressor\n");
+		return -EIO;
+	}
+
+	out_buf.size = PAGE_SIZE;
+	out_buf.dst = squashfs_first_page(output);
+	if (IS_ERR(out_buf.dst)) {
+		error = PTR_ERR(out_buf.dst);
+		goto finish;
+	}
+
+	for (;;) {
+		size_t zstd_err;
+
+		if (in_buf.pos == in_buf.size) {
+			const void *data;
+			int avail;
+
+			if (!bio_next_segment(bio, &iter_all)) {
+				error = -EIO;
+				break;
+			}
+
+			avail = min(length, ((int)bvec->bv_len) - offset);
+			data = bvec_virt(bvec);
+			length -= avail;
+			in_buf.src = data + offset;
+			in_buf.size = avail;
+			in_buf.pos = 0;
+			offset = 0;
+		}
+
+		if (out_buf.pos == out_buf.size) {
+			out_buf.dst = squashfs_next_page(output);
+			if (IS_ERR(out_buf.dst)) {
+				error = PTR_ERR(out_buf.dst);
+				break;
+			} else if (out_buf.dst == NULL) {
+				/* Shouldn't run out of pages
+				 * before stream is done.
+				 */
+				error = -EIO;
+				break;
+			}
+			out_buf.pos = 0;
+			out_buf.size = PAGE_SIZE;
+		}
+
+		total_out -= out_buf.pos;
+		zstd_err = zstd_decompress_stream(stream, &out_buf, &in_buf);
+		total_out += out_buf.pos; /* add the additional data produced */
+		if (zstd_err == 0)
+			break;
+
+		if (zstd_is_error(zstd_err)) {
+			ERROR("zstd decompression error: %d\n",
+					(int)zstd_get_error_code(zstd_err));
+			error = -EIO;
+			break;
+		}
+	}
+
+finish:
+
+	squashfs_finish_page(output);
+
+	return error ? error : total_out;
+}
+
+const struct squashfs_decompressor squashfs_zstd_comp_ops = {
+	.init = zstd_init,
+	.free = zstd_free,
+	.decompress = zstd_uncompress,
+	.id = ZSTD_COMPRESSION,
+	.name = "zstd",
+	.alloc_buffer = 1,
+	.supported = 1
+};