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, 76 insertions, 0 deletions

diff --git a/sound/soc/sof/sof-utils.c b/sound/soc/sof/sof-utils.c
new file mode 100644
index 000000000..f70089317
--- /dev/null
+++ b/sound/soc/sof/sof-utils.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+//
+// This file is provided under a dual BSD/GPLv2 license.  When using or
+// redistributing this file, you may do so under either license.
+//
+// Copyright(c) 2018-2022 Intel Corporation
+//
+// Author: Keyon Jie <yang.jie@linux.intel.com>
+//
+
+#include <linux/unaligned.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
+#include <linux/device.h>
+#include <sound/memalloc.h>
+#include <linux/module.h>
+#include "sof-utils.h"
+
+/*
+ * Generic buffer page table creation.
+ * Take the each physical page address and drop the least significant unused
+ * bits from each (based on PAGE_SIZE). Then pack valid page address bits
+ * into compressed page table.
+ */
+
+int snd_sof_create_page_table(struct device *dev,
+			      struct snd_dma_buffer *dmab,
+			      unsigned char *page_table, size_t size)
+{
+	int i, pages;
+
+	pages = snd_sgbuf_aligned_pages(size);
+
+	dev_dbg(dev, "generating page table for %p size 0x%zx pages %d\n",
+		dmab->area, size, pages);
+
+	for (i = 0; i < pages; i++) {
+		/*
+		 * The number of valid address bits for each page is 20.
+		 * idx determines the byte position within page_table
+		 * where the current page's address is stored
+		 * in the compressed page_table.
+		 * This can be calculated by multiplying the page number by 2.5.
+		 */
+		u32 idx = (5 * i) >> 1;
+		u32 pfn = snd_sgbuf_get_addr(dmab, i * PAGE_SIZE) >> PAGE_SHIFT;
+		u8 *pg_table;
+
+		pg_table = (u8 *)(page_table + idx);
+
+		/*
+		 * pagetable compression:
+		 * byte 0     byte 1     byte 2     byte 3     byte 4     byte 5
+		 * ___________pfn 0__________ __________pfn 1___________  _pfn 2...
+		 * .... ....  .... ....  .... ....  .... ....  .... ....  ....
+		 * It is created by:
+		 * 1. set current location to 0, PFN index i to 0
+		 * 2. put pfn[i] at current location in Little Endian byte order
+		 * 3. calculate an intermediate value as
+		 *    x = (pfn[i+1] << 4) | (pfn[i] & 0xf)
+		 * 4. put x at offset (current location + 2) in LE byte order
+		 * 5. increment current location by 5 bytes, increment i by 2
+		 * 6. continue to (2)
+		 */
+		if (i & 1)
+			put_unaligned_le32((pg_table[0] & 0xf) | pfn << 4,
+					   pg_table);
+		else
+			put_unaligned_le32(pfn, pg_table);
+	}
+
+	return pages;
+}
+EXPORT_SYMBOL(snd_sof_create_page_table);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("SOF utils");