[PATCH v2 06/19] crypto: x86/sm3 - limit FPU preemption

[Robert Elliott]

As done by the ECB and CBC helpers in arch/x86/crypt/ecb_cbc_helpers.h,
limit the number of bytes processed between kernel_fpu_begin() and
kernel_fpu_end() calls.

Those functions call preempt_disable() and preempt_enable(), so
the CPU core is unavailable for scheduling while running, causing:
    rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: ...

Fixes: 930ab34d906d ("crypto: x86/sm3 - add AVX assembly implementation")
Suggested-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Robert Elliott <elliott@xxxxxxx>
---
 arch/x86/crypto/sm3_avx_glue.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/x86/crypto/sm3_avx_glue.c b/arch/x86/crypto/sm3_avx_glue.c
index 661b6f22ffcd..ffb6d2f409ef 100644
--- a/arch/x86/crypto/sm3_avx_glue.c
+++ b/arch/x86/crypto/sm3_avx_glue.c
@@ -17,6 +17,8 @@
 #include <crypto/sm3_base.h>
 #include <asm/simd.h>
 
+#define FPU_BYTES 4096U /* avoid kernel_fpu_begin/end scheduler/rcu stalls */
+
 asmlinkage void sm3_transform_avx(struct sm3_state *state,
 			const u8 *data, int nblocks);
 
@@ -37,9 +39,16 @@ static int sm3_avx_update(struct shash_desc *desc, const u8 *data,
 	 */
 	BUILD_BUG_ON(offsetof(struct sm3_state, state) != 0);
 
-	kernel_fpu_begin();
-	sm3_base_do_update(desc, data, len, sm3_transform_avx);
-	kernel_fpu_end();
+	do {
+		unsigned int chunk = min(len, FPU_BYTES);
+
+		kernel_fpu_begin();
+		sm3_base_do_update(desc, data, chunk, sm3_transform_avx);
+		kernel_fpu_end();
+
+		len -= chunk;
+		data += chunk;
+	} while (len);
 
 	return 0;
 }
@@ -57,9 +66,19 @@ static int sm3_avx_finup(struct shash_desc *desc, const u8 *data,
 		return 0;
 	}
 
+	do {
+		unsigned int chunk = min(len, FPU_BYTES);
+
+		if (chunk) {
+			kernel_fpu_begin();
+			sm3_base_do_update(desc, data, chunk, sm3_transform_avx);
+			kernel_fpu_end();
+		}
+
+		len -= chunk;
+		data += chunk;
+	} while (len);
 	kernel_fpu_begin();
-	if (len)
-		sm3_base_do_update(desc, data, len, sm3_transform_avx);
 	sm3_base_do_finalize(desc, sm3_transform_avx);
 	kernel_fpu_end();
 
-- 
2.37.3