crypto: caam - never share the gcm and skcipher descriptors serially

RFC PATCH In review Vincent Jardin 2 participants 3 messages Nov 8 – Nov 9

Subsystems (2)

Crypto API Freescale CAAM (Cryptographic Acceleration and Assurance Module) driver

lore

Share & tools

lore

Vincent Jardin

author

2026-11-08 23:42 UTC #0 lore raw

RFC PATCH 1/1 crypto: caam - never share the gcm and skcipher descriptors serially

The gcm and skcipher shared descriptors were built with HDR_SHARE_SERIAL, so the SEC runs the jobs of one key one after the other:
it leads to about 4 Gbps per key on LX2160A, whatever the number of CPUs or queues. No hardware reason for this code has been found.

From benchmarks, when built with HDR_SHARE_NEVER, the performance is much better and scales: for instance with one CPU, AES-128-GCM, the gains are:
- 325 -> 592 MB/s at 1420 B
- 498 -> 6283 MB/s at 16 KiB

Signed-off-by Vincent Jardin <[email protected]>

---
 drivers/crypto/caam/caamalg_desc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

drivers/crypto/caam/caamalg_desc.c +4 -4

index 04c1105eb1f5..32d614a3431d 100644
@@ -639,7 +639,7 @@ void cnstr_shdsc_gcm_encap(u32 * const desc, struct alginfo *cdata,
 	u32 *key_jump_cmd, *zero_payload_jump_cmd, *zero_assoc_jump_cmd1,
 	    *zero_assoc_jump_cmd2;
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL);
+	init_sh_desc(desc, HDR_SHARE_NEVER);
 
 	/* skip key loading if they are loaded due to sharing */
 	key_jump_cmd = append_jump(desc, JUMP_JSL | JUMP_TEST_ALL |

@@ -765,7 +765,7 @@ void cnstr_shdsc_gcm_decap(u32 * const desc, struct alginfo *cdata,
 {
 	u32 *key_jump_cmd, *zero_payload_jump_cmd, *zero_assoc_jump_cmd1;
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL);
+	init_sh_desc(desc, HDR_SHARE_NEVER);
 
 	/* skip key loading if they are loaded due to sharing */
 	key_jump_cmd = append_jump(desc, JUMP_JSL |

@@ -1463,7 +1463,7 @@ void cnstr_shdsc_skcipher_encap(u32 * const desc, struct alginfo *cdata,
 	bool is_chacha20 = ((cdata->algtype & OP_ALG_ALGSEL_MASK) ==
 			    OP_ALG_ALGSEL_CHACHA20);
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL | HDR_SAVECTX);
+	init_sh_desc(desc, HDR_SHARE_NEVER | HDR_SAVECTX);
 	/* Skip if already shared */
 	key_jump_cmd = append_jump(desc, JUMP_JSL | JUMP_TEST_ALL |
 				   JUMP_COND_SHRD);

@@ -1539,7 +1539,7 @@ void cnstr_shdsc_skcipher_decap(u32 * const desc, struct alginfo *cdata,
 	bool is_chacha20 = ((cdata->algtype & OP_ALG_ALGSEL_MASK) ==
 			    OP_ALG_ALGSEL_CHACHA20);
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL | HDR_SAVECTX);
+	init_sh_desc(desc, HDR_SHARE_NEVER | HDR_SAVECTX);
 	/* Skip if already shared */
 	key_jump_cmd = append_jump(desc, JUMP_JSL | JUMP_TEST_ALL |
 				   JUMP_COND_SHRD);

---
base-commit: 82e91fe19fb838f235f7c8829afc1eb389c93bdf
change-id: 20261108-for-upstream-caam-shdsc-share-never-v1-e6f7f5e0ad23

Best regards,

Signature · 1 line

Vincent Jardin <[email protected]>

[email protected]

AI review

2026-11-08 23:55 UTC #1 lore raw

Thank you for your contribution! Sashiko AI review found 1 potential issue to consider: - [Low] crypto: caam: dead sharing jumps and HDR_SAVECTX with HDR_SHARE_NEVER --

Thank you for your contribution! Sashiko AI review found 1 potential issue to consider:
- [Low] crypto: caam: dead sharing jumps and HDR_SAVECTX with HDR_SHARE_NEVER
--

commit 9b09bbe924ba4f39f4ea4b61b1bb908c38315173
Author: Vincent Jardin <[email protected]>

crypto: caam - never share the gcm and skcipher descriptors serially

This commit changes the GCM and skcipher shared descriptors from HDR_SHARE_SERIAL to HDR_SHARE_NEVER so jobs using the same key are not serialized by the SEC hardware.

Quoted 32 lines

drivers/crypto/caam/caamalg_desc.c +3 -3

index 04c1105eb1f58..32d614a3431da 100644
@@ -639,7 +639,7 @@ void cnstr_shdsc_gcm_encap(u32 * const desc, struct alginfo *cdata,
 	u32 *key_jump_cmd, *zero_payload_jump_cmd, *zero_assoc_jump_cmd1,
 	    *zero_assoc_jump_cmd2;
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL);
+	init_sh_desc(desc, HDR_SHARE_NEVER);
 
 	/* skip key loading if they are loaded due to sharing */
 	key_jump_cmd = append_jump(desc, JUMP_JSL | JUMP_TEST_ALL |

@@ -765,7 +765,7 @@ void cnstr_shdsc_gcm_decap(u32 * const desc, struct alginfo *cdata,
 {
 	u32 *key_jump_cmd, *zero_payload_jump_cmd, *zero_assoc_jump_cmd1;
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL);
+	init_sh_desc(desc, HDR_SHARE_NEVER);
 
 	/* skip key loading if they are loaded due to sharing */
 	key_jump_cmd = append_jump(desc, JUMP_JSL |

@@ -1463,7 +1463,7 @@ void cnstr_shdsc_skcipher_encap(u32 * const desc, struct alginfo *cdata,
 	bool is_chacha20 = ((cdata->algtype & OP_ALG_ALGSEL_MASK) ==
 			    OP_ALG_ALGSEL_CHACHA20);
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL | HDR_SAVECTX);
+	init_sh_desc(desc, HDR_SHARE_NEVER | HDR_SAVECTX);
 	/* Skip if already shared */
 	key_jump_cmd = append_jump(desc, JUMP_JSL | JUMP_TEST_ALL |
 				   JUMP_COND_SHRD);

drivers/crypto/caam/caamalg_desc.c void cnstr_shdsc_skcipher_decap(u32 * const desc, struct alginfo *cdata, · line 1545

Quoted 8 lines

drivers/crypto/caam/caamalg_desc.c +1 -1

@@ -1539,7 +1539,7 @@ void cnstr_shdsc_skcipher_decap(u32 * const desc, struct alginfo *cdata,
 	bool is_chacha20 = ((cdata->algtype & OP_ALG_ALGSEL_MASK) ==
 			    OP_ALG_ALGSEL_CHACHA20);
 
-	init_sh_desc(desc, HDR_SHARE_SERIAL | HDR_SAVECTX);
+	init_sh_desc(desc, HDR_SHARE_NEVER | HDR_SAVECTX);
 	/* Skip if already shared */
 	key_jump_cmd = append_jump(desc, JUMP_JSL | JUMP_TEST_ALL |
 				   JUMP_COND_SHRD);

[Severity: Low]
With HDR_SHARE_NEVER, should HDR_SAVECTX and the JUMP_COND_SHRD jumps also be dropped from these four descriptors?

All CAAM job backends defer sharing mode to the shared descriptor header, so HDR_SHARE_NEVER disables descriptor sharing across jobs and JUMP_COND_SHRD is never true. Keeping key_jump_cmd and the JUMP_COND_SHRD branch in append_dec_op1() called by cnstr_shdsc_skcipher_decap() leaves unreachable instructions in the descriptors that waste space and DECO cycles on every job, and HDR_SAVECTX only applies when a descriptor is self-shared.

Signature · 1 line

Sashiko AI review · https://sashiko.dev/#/patchset/20261109-for-upstream-caam-shdsc-share-never-v1-v1-1-65a1dd146db2@free.fr?part=1

Vincent Jardin

author

2026-11-09 09:24 UTC #2 lore raw

Hi Mx Bot,

Quoted 10 lines

[Severity: Low]
With HDR_SHARE_NEVER, should HDR_SAVECTX and the JUMP_COND_SHRD jumps also be dropped from these four descriptors?
All CAAM job backends defer sharing mode to the shared descriptor header, so HDR_SHARE_NEVER disables descriptor sharing across jobs and JUMP_COND_SHRD is never true. Keeping key_jump_cmd and the JUMP_COND_SHRD branch in append_dec_op1() called by cnstr_shdsc_skcipher_decap() leaves unreachable instructions in the descriptors that waste space and DECO cycles on every job, and HDR_SAVECTX only applies when a descriptor is self-shared.

Right, both are void under HDR_SHARE_NEVER: the SHRD condition never holds, and Save Context only acts under serial self-sharing (SEC RM, HEADER command).

They are here on purpose for this RFC: to focus on the change under discussion.

Quoted 3 lines

Signature · 2 lines

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261109-for-upstream-caam-shdsc-share-never-v1-v1-1-65a1dd146db2@free.fr?part=1