[PATCH v3 00/21] arm64: Move kernel mode FPSIMD buffer to the stack

[Eric Biggers]

On Wed, Oct 08, 2025 at 05:45:34PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb at kernel.org>
> 
> Move the buffer for preserving/restoring the kernel mode FPSIMD state on a
> context switch out of struct thread_struct, and onto the stack, so that
> the memory cost is not imposed needlessly on all tasks in the system.

This patchset needs the following fixup to build:

diff --git a/lib/crc/arm/crc-t10dif.h b/lib/crc/arm/crc-t10dif.h
index 7f02a767f675e..aaeeab0defb5d 100644
--- a/lib/crc/arm/crc-t10dif.h
+++ b/lib/crc/arm/crc-t10dif.h
@@ -17,11 +17,11 @@ asmlinkage void crc_t10dif_pmull8(u16 init_crc, const u8 *buf, size_t len,
 				  u8 out[16]);
 
 static inline u16 crc_t10dif_arch(u16 crc, const u8 *data, size_t length)
 {
 	if (length >= CRC_T10DIF_PMULL_CHUNK_SIZE) {
-		if (static_branch_likely(&have_pmull) && likely(may_use_simd()) {
+		if (static_branch_likely(&have_pmull) && likely(may_use_simd())) {
 			scoped_ksimd()
 				return crc_t10dif_pmull64(crc, data, length);
 		} else if (length > CRC_T10DIF_PMULL_CHUNK_SIZE &&
 			   static_branch_likely(&have_neon) &&
 			   likely(may_use_simd())) {
diff --git a/lib/crypto/arm/sha512.h b/lib/crypto/arm/sha512.h
index 8d3af965d2b34..ed9bd81d6d78d 100644
--- a/lib/crypto/arm/sha512.h
+++ b/lib/crypto/arm/sha512.h
@@ -16,10 +16,11 @@ asmlinkage void sha512_block_data_order_neon(struct sha512_block_state *state,
 
 static void sha512_blocks(struct sha512_block_state *state,
 			  const u8 *data, size_t nblocks)
 {
 	if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) &&
+	    static_branch_likely(&have_neon) && likely(may_use_simd())) {
 		scoped_ksimd()
 			sha512_block_data_order_neon(state, data, nblocks);
 	} else {
 		sha512_block_data_order(state, data, nblocks);
 	}