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, 94 insertions, 0 deletions

diff --git a/include/crypto/aes-xts.h b/include/crypto/aes-xts.h
new file mode 100644
index 000000000..b9e828265
--- /dev/null
+++ b/include/crypto/aes-xts.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * AES-XTS unauthenticated encryption and decryption
+ *
+ * Copyright 2026 Google LLC
+ */
+#ifndef _CRYPTO_AES_XTS_H
+#define _CRYPTO_AES_XTS_H
+
+#include <crypto/aes.h>
+#include <crypto/xts.h>
+
+/**
+ * struct aes_xts_key - A key prepared for AES-XTS encryption and decryption
+ *
+ * Note that (depending on the architecture) this typically is around 768 bytes,
+ * which makes it a bit too large to allocate on the stack in most cases.
+ */
+struct aes_xts_key {
+	/* private: */
+	struct aes_key main_key;
+	struct aes_enckey tweak_key;
+};
+
+/**
+ * aes_xts_preparekey() - Prepare a key for AES-XTS encryption and decryption
+ * @key: (output) The key structure to initialize
+ * @in_key: The raw AES-XTS key
+ * @key_len: Length of the raw key in bytes
+ * @flags: Optional flag XTS_FORBID_WEAK_KEYS to forbid keys whose two halves
+ *	   are the same.
+ *
+ * Users should use memzero_explicit() to zeroize the key struct at the end of
+ * its lifetime.  (But if this function fails, zeroization is unnecessary.)
+ *
+ * Context: Any context.
+ * Return:
+ * * 0 on success
+ * * -EINVAL if the key is rejected because its length isn't 32, 64, or (when
+ *   FIPS mode isn't enabled) 48; or because its two halves are the same and
+ *   either XTS_FORBID_WEAK_KEYS is given or FIPS mode is enabled.
+ */
+int __must_check aes_xts_preparekey(struct aes_xts_key *key, const u8 *in_key,
+				    size_t key_len, int flags);
+
+/**
+ * aes_xts_encrypt() - Encrypt data using AES-XTS
+ * @dst: The destination buffer.  Can be in-place or out-of-place.  For other
+ *	 overlaps the behavior is unspecified.
+ * @src: The source data
+ * @len: Number of bytes to encrypt.  On non-final calls it must be a nonzero
+ *	 multiple of AES_BLOCK_SIZE.  On the final call it can be any value >=
+ *	 AES_BLOCK_SIZE, i.e. ciphertext stealing is supported.
+ * @tweak: The tweak.  It is updated with the next value, unless @len isn't a
+ *	   multiple of AES_BLOCK_SIZE in which case the value is unspecified.
+ * @key: The key, already prepared using aes_xts_preparekey()
+ * @cont: %false to begin encrypting a new message (do the tweak encryption);
+ *	  %true to continue encrypting a message (skip tweak encryption)
+ *
+ * This supports both one-shot and incremental encryption.  On the first call,
+ * pass @cont = %false.  On any later calls, pass @cont = %true and the updated
+ * @tweak; all earlier @len must have been multiples of AES_BLOCK_SIZE.
+ *
+ * Context: Any context.
+ */
+void aes_xts_encrypt(u8 *dst, const u8 *src, size_t len,
+		     u8 tweak[at_least AES_BLOCK_SIZE],
+		     const struct aes_xts_key *key, bool cont);
+
+/**
+ * aes_xts_decrypt() - Decrypt data using AES-XTS
+ * @dst: The destination buffer.  Can be in-place or out-of-place.  For other
+ *	 overlaps the behavior is unspecified.
+ * @src: The source data
+ * @len: Number of bytes to decrypt.  On non-final calls it must be a nonzero
+ *	 multiple of AES_BLOCK_SIZE.  On the final call it can be any value >=
+ *	 AES_BLOCK_SIZE, i.e. ciphertext stealing is supported.
+ * @tweak: The tweak.  It is updated with the next value, unless @len isn't a
+ *	   multiple of AES_BLOCK_SIZE in which case the value is unspecified.
+ * @key: The key, already prepared using aes_xts_preparekey()
+ * @cont: %false to begin decrypting a new message (do the tweak encryption);
+ *	  %true to continue decrypting a message (skip tweak encryption)
+ *
+ * This supports both one-shot and incremental decryption.  On the first call,
+ * pass @cont = %false.  On any later calls, pass @cont = %true and the updated
+ * @tweak; all earlier @len must have been multiples of AES_BLOCK_SIZE.
+ *
+ * Context: Any context.
+ */
+void aes_xts_decrypt(u8 *dst, const u8 *src, size_t len,
+		     u8 tweak[at_least AES_BLOCK_SIZE],
+		     const struct aes_xts_key *key, bool cont);
+
+#endif /* _CRYPTO_AES_XTS_H */