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, 25 insertions, 0 deletions

diff --git a/include/crypto/twofish.h b/include/crypto/twofish.h
new file mode 100644
index 000000000..f6b307a58
--- /dev/null
+++ b/include/crypto/twofish.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _CRYPTO_TWOFISH_H
+#define _CRYPTO_TWOFISH_H
+
+#include <linux/types.h>
+
+#define TF_MIN_KEY_SIZE 16
+#define TF_MAX_KEY_SIZE 32
+#define TF_BLOCK_SIZE 16
+
+struct crypto_tfm;
+
+/* Structure for an expanded Twofish key.  s contains the key-dependent
+ * S-boxes composed with the MDS matrix; w contains the eight "whitening"
+ * subkeys, K[0] through K[7].	k holds the remaining, "round" subkeys.  Note
+ * that k[i] corresponds to what the Twofish paper calls K[i+8]. */
+struct twofish_ctx {
+	u32 s[4][256], w[8], k[32];
+};
+
+int __twofish_setkey(struct twofish_ctx *ctx, const u8 *key,
+		     unsigned int key_len);
+int twofish_setkey(struct crypto_tfm *tfm, const u8 *key, unsigned int key_len);
+
+#endif