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, 52 insertions, 0 deletions

diff --git a/include/crypto/nh.h b/include/crypto/nh.h
new file mode 100644
index 000000000..465e85bf2
--- /dev/null
+++ b/include/crypto/nh.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * NH hash function for Adiantum
+ */
+
+#ifndef _CRYPTO_NH_H
+#define _CRYPTO_NH_H
+
+#include <linux/types.h>
+
+/* NH parameterization: */
+
+/* Endianness: little */
+/* Word size: 32 bits (works well on NEON, SSE2, AVX2) */
+
+/* Stride: 2 words (optimal on ARM32 NEON; works okay on other CPUs too) */
+#define NH_PAIR_STRIDE		2
+#define NH_MESSAGE_UNIT		(NH_PAIR_STRIDE * 2 * sizeof(u32))
+
+/* Num passes (Toeplitz iteration count): 4, to give ε = 2^{-128} */
+#define NH_NUM_PASSES		4
+#define NH_HASH_BYTES		(NH_NUM_PASSES * sizeof(u64))
+
+/* Max message size: 1024 bytes (32x compression factor) */
+#define NH_NUM_STRIDES		64
+#define NH_MESSAGE_WORDS	(NH_PAIR_STRIDE * 2 * NH_NUM_STRIDES)
+#define NH_MESSAGE_BYTES	(NH_MESSAGE_WORDS * sizeof(u32))
+#define NH_KEY_WORDS		(NH_MESSAGE_WORDS + \
+				 NH_PAIR_STRIDE * 2 * (NH_NUM_PASSES - 1))
+#define NH_KEY_BYTES		(NH_KEY_WORDS * sizeof(u32))
+
+/**
+ * nh() - NH hash function for Adiantum
+ * @key: The key.  @message_len + 48 bytes of it are used.  This is NH_KEY_BYTES
+ *	 if @message_len has its maximum length of NH_MESSAGE_BYTES.
+ * @message: The message
+ * @message_len: The message length in bytes.  Must be a multiple of 16
+ *		 (NH_MESSAGE_UNIT) and at most 1024 (NH_MESSAGE_BYTES).
+ * @hash: (output) The resulting hash value
+ *
+ * Note: the pseudocode for NH in the Adiantum paper iterates over 1024-byte
+ * segments of the message, computes a 32-byte hash for each, and returns all
+ * the hashes concatenated together.  In contrast, this function just hashes one
+ * segment and returns one hash.  It's the caller's responsibility to call this
+ * function for each 1024-byte segment and collect all the hashes.
+ *
+ * Context: Any context.
+ */
+void nh(const u32 *key, const u8 *message, size_t message_len,
+	__le64 hash[NH_NUM_PASSES]);
+
+#endif /* _CRYPTO_NH_H */