KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 137 insertions, 0 deletions

diff --git a/fs/squashfs/zlib_wrapper.c b/fs/squashfs/zlib_wrapper.c
new file mode 100644
index 000000000..a29001311
--- /dev/null
+++ b/fs/squashfs/zlib_wrapper.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Squashfs - a compressed read only filesystem for Linux
+ *
+ * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
+ * Phillip Lougher <phillip@squashfs.org.uk>
+ *
+ * zlib_wrapper.c
+ */
+
+
+#include <linux/mutex.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/zlib.h>
+#include <linux/vmalloc.h>
+
+#include "squashfs_fs.h"
+#include "squashfs_fs_sb.h"
+#include "squashfs.h"
+#include "decompressor.h"
+#include "page_actor.h"
+
+static void *zlib_init(struct squashfs_sb_info *dummy, void *buff)
+{
+	z_stream *stream = kmalloc_obj(z_stream);
+	if (stream == NULL)
+		goto failed;
+	stream->workspace = vmalloc(zlib_inflate_workspacesize());
+	if (stream->workspace == NULL)
+		goto failed;
+
+	return stream;
+
+failed:
+	ERROR("Failed to allocate zlib workspace\n");
+	kfree(stream);
+	return ERR_PTR(-ENOMEM);
+}
+
+
+static void zlib_free(void *strm)
+{
+	z_stream *stream = strm;
+
+	if (stream)
+		vfree(stream->workspace);
+	kfree(stream);
+}
+
+
+static int zlib_uncompress(struct squashfs_sb_info *msblk, void *strm,
+	struct bio *bio, int offset, int length,
+	struct squashfs_page_actor *output)
+{
+	struct bvec_iter_all iter_all = {};
+	struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
+	int zlib_init = 0, error = 0;
+	z_stream *stream = strm;
+
+	stream->avail_out = PAGE_SIZE;
+	stream->next_out = squashfs_first_page(output);
+	stream->avail_in = 0;
+
+	if (IS_ERR(stream->next_out)) {
+		error = PTR_ERR(stream->next_out);
+		goto finish;
+	}
+
+	for (;;) {
+		int zlib_err;
+
+		if (stream->avail_in == 0) {
+			const void *data;
+			int avail;
+
+			if (!bio_next_segment(bio, &iter_all)) {
+				/* Z_STREAM_END must be reached. */
+				error = -EIO;
+				break;
+			}
+
+			avail = min(length, ((int)bvec->bv_len) - offset);
+			data = bvec_virt(bvec);
+			length -= avail;
+			stream->next_in = data + offset;
+			stream->avail_in = avail;
+			offset = 0;
+		}
+
+		if (stream->avail_out == 0) {
+			stream->next_out = squashfs_next_page(output);
+			if (IS_ERR(stream->next_out)) {
+				error = PTR_ERR(stream->next_out);
+				break;
+			} else if (stream->next_out != NULL)
+				stream->avail_out = PAGE_SIZE;
+		}
+
+		if (!zlib_init) {
+			zlib_err = zlib_inflateInit(stream);
+			if (zlib_err != Z_OK) {
+				error = -EIO;
+				break;
+			}
+			zlib_init = 1;
+		}
+
+		zlib_err = zlib_inflate(stream, Z_SYNC_FLUSH);
+		if (zlib_err == Z_STREAM_END)
+			break;
+		if (zlib_err != Z_OK) {
+			error = -EIO;
+			break;
+		}
+	}
+
+finish:
+	squashfs_finish_page(output);
+
+	if (!error)
+		if (zlib_inflateEnd(stream) != Z_OK)
+			error = -EIO;
+
+	return error ? error : stream->total_out;
+}
+
+const struct squashfs_decompressor squashfs_zlib_comp_ops = {
+	.init = zlib_init,
+	.free = zlib_free,
+	.decompress = zlib_uncompress,
+	.id = ZLIB_COMPRESSION,
+	.name = "zlib",
+	.alloc_buffer = 1,
+	.supported = 1
+};
+