linux-kernel - [PATCH] x86/crc32: optimize tail handling for crc32c short inputs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250304213216.108925-1-ebiggers@kernel.org>
Date: Tue,  4 Mar 2025 13:32:16 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Bill Wendling <morbo@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Justin Stitt <justinstitt@...gle.com>,
	David Laight <david.laight.linux@...il.com>,
	linux-crypto@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] x86/crc32: optimize tail handling for crc32c short inputs

From: Eric Biggers <ebiggers@...gle.com>

For handling the 0 <= len < sizeof(unsigned long) bytes left at the end,
do a 4-2-1 step-down instead of a byte-at-a-time loop.  This allows
taking advantage of wider CRC instructions.  Note that crc32c-3way.S
already uses this same optimization too.

crc_kunit shows an improvement of about 25% for len=127.

Suggested-by: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---

This applies to
https://web.git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=crc-next

 arch/x86/lib/crc32-glue.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/lib/crc32-glue.c b/arch/x86/lib/crc32-glue.c
index 4b4721176799a..e3f93b17ac3f1 100644
--- a/arch/x86/lib/crc32-glue.c
+++ b/arch/x86/lib/crc32-glue.c
@@ -55,11 +55,19 @@ u32 crc32c_arch(u32 crc, const u8 *p, size_t len)
 
 	for (num_longs = len / sizeof(unsigned long);
 	     num_longs != 0; num_longs--, p += sizeof(unsigned long))
 		asm(CRC32_INST : "+r" (crc) : ASM_INPUT_RM (*(unsigned long *)p));
 
-	for (len %= sizeof(unsigned long); len; len--, p++)
+	if (sizeof(unsigned long) > 4 && (len & 4)) {
+		asm("crc32l %1, %0" : "+r" (crc) : ASM_INPUT_RM (*(u32 *)p));
+		p += 4;
+	}
+	if (len & 2) {
+		asm("crc32w %1, %0" : "+r" (crc) : ASM_INPUT_RM (*(u16 *)p));
+		p += 2;
+	}
+	if (len & 1)
 		asm("crc32b %1, %0" : "+r" (crc) : ASM_INPUT_RM (*p));
 
 	return crc;
 }
 EXPORT_SYMBOL(crc32c_arch);

base-commit: 13f3d13d88b5dcba104a204fcbee61c75f8407d0
-- 
2.48.1