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, 96 insertions, 0 deletions

diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
new file mode 100644
index 000000000..81a0f3f6f
--- /dev/null
+++ b/drivers/block/zram/zcomp.h
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _ZCOMP_H_
+#define _ZCOMP_H_
+
+#include <linux/mutex.h>
+
+#define ZCOMP_PARAM_NOT_SET	INT_MIN
+
+struct deflate_params {
+	s32 winbits;
+};
+
+/*
+ * Immutable driver (backend) parameters. The driver may attach private
+ * data to it (e.g. driver representation of the dictionary, etc.).
+ *
+ * This data is kept per-comp and is shared among execution contexts.
+ */
+struct zcomp_params {
+	void *dict;
+	size_t dict_sz;
+	s32 level;
+	union {
+		struct deflate_params deflate;
+	};
+
+	void *drv_data;
+};
+
+/*
+ * Run-time driver context - scratch buffers, etc. It is modified during
+ * request execution (compression/decompression), cannot be shared, so
+ * it's in per-CPU area.
+ */
+struct zcomp_ctx {
+	void *context;
+};
+
+struct zcomp_strm {
+	struct mutex lock;
+	/* compression buffer */
+	void *buffer;
+	/* local copy of handle memory */
+	void *local_copy;
+	struct zcomp_ctx ctx;
+};
+
+struct zcomp_req {
+	const unsigned char *src;
+	const size_t src_len;
+
+	unsigned char *dst;
+	size_t dst_len;
+};
+
+struct zcomp_ops {
+	int (*compress)(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			struct zcomp_req *req);
+	int (*decompress)(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			  struct zcomp_req *req);
+
+	int (*create_ctx)(struct zcomp_params *params, struct zcomp_ctx *ctx);
+	void (*destroy_ctx)(struct zcomp_ctx *ctx);
+
+	int (*setup_params)(struct zcomp_params *params);
+	void (*release_params)(struct zcomp_params *params);
+
+	const char *name;
+};
+
+/* dynamic per-device compression frontend */
+struct zcomp {
+	struct zcomp_strm __percpu *stream;
+	const struct zcomp_ops *ops;
+	struct zcomp_params *params;
+	struct hlist_node node;
+};
+
+int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node);
+int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node);
+ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at);
+const char *zcomp_lookup_backend_name(const char *comp);
+
+struct zcomp *zcomp_create(const char *alg, struct zcomp_params *params);
+void zcomp_destroy(struct zcomp *comp);
+
+struct zcomp_strm *zcomp_stream_get(struct zcomp *comp);
+void zcomp_stream_put(struct zcomp_strm *zstrm);
+
+int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		   const void *src, unsigned int *dst_len);
+int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		     const void *src, unsigned int src_len, void *dst);
+
+#endif /* _ZCOMP_H_ */