linux-kernel - Re: [PATCH] crypto: x86/crc32c-intel

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Message-ID: <20201215085819.GE3040@hirez.programming.kicks-ass.net>
Date:   Tue, 15 Dec 2020 09:58:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tony W Wang-oc <TonyWWang-oc@...oxin.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, TimGuo-oc@...oxin.com,
        CooperYan@...oxin.com, QiyuanWang@...oxin.com,
        HerryYang@...oxin.com, CobeChen@...oxin.com, SilviaZhao@...oxin.com
Subject: Re: [PATCH] crypto: x86/crc32c-intel - Don't match some Zhaoxin CPUs

On Mon, Dec 14, 2020 at 11:59:52AM +0800, Tony W Wang-oc wrote:

Didn't I mention something about a comment?

>  static const struct x86_cpu_id crc32c_cpu_id[] = {
> +	X86_MATCH_VENDOR_FAM_FEATURE(ZHAOXIN, 0x6, X86_FEATURE_XMM4_2, 1),
> +	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(ZHAOXIN, 0x7, 0x1b, X86_FEATURE_XMM4_2, 1),
> +	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(ZHAOXIN, 0x7, 0x3b, X86_FEATURE_XMM4_2, 1),
> +	X86_MATCH_VENDOR_FAM_FEATURE(CENTAUR, 0x6, X86_FEATURE_XMM4_2, 1),
> +	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(CENTAUR, 0x7, 0x1b, X86_FEATURE_XMM4_2, 1),
> +	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(CENTAUR, 0x7, 0x3b, X86_FEATURE_XMM4_2, 1),
>  	X86_MATCH_FEATURE(X86_FEATURE_XMM4_2, NULL),
>  	{}

Also, the above is weird in that is has the negative entries marked
positive, and 1/NULL are inconsistent.

Something like so then?

---

diff --git a/arch/x86/crypto/crc32c-intel_glue.c b/arch/x86/crypto/crc32c-intel_glue.c
index feccb5254c7e..f6e6669a5102 100644
--- a/arch/x86/crypto/crc32c-intel_glue.c
+++ b/arch/x86/crypto/crc32c-intel_glue.c
@@ -215,14 +215,31 @@ static struct shash_alg alg = {
 };
 
 static const struct x86_cpu_id crc32c_cpu_id[] = {
-	X86_MATCH_FEATURE(X86_FEATURE_XMM4_2, NULL),
+	/*
+	 * Negative entries; exclude these chips from using this driver.
+	 * They match the positive rule below, but their CRC32 instruction
+	 * implementation is so slow, it doesn't merrit use.
+	 */
+	X86_MATCH_VENDOR_FAM_FEATURE(ZHAOXIN, 0x6, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(ZHAOXIN, 0x7, 0x1b, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(ZHAOXIN, 0x7, 0x3b, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_FEATURE(CENTAUR, 0x6, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(CENTAUR, 0x7, 0x1b, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(CENTAUR, 0x7, 0x3b, X86_FEATURE_XMM4_2, false),
+	/*
+	 * Positive entry; SSE-4.2 instructions include special purpose CRC32
+	 * instructions.
+	 */
+	X86_MATCH_FEATURE(X86_FEATURE_XMM4_2, true),
 	{}
 };
 MODULE_DEVICE_TABLE(x86cpu, crc32c_cpu_id);
 
 static int __init crc32c_intel_mod_init(void)
 {
-	if (!x86_match_cpu(crc32c_cpu_id))
+	const struct x86_cpu_id *m = x86_match_cpu(crc32c_cpu_id);
+
+	if (!m || !m->driver_data)
 		return -ENODEV;
 #ifdef CONFIG_X86_64
 	if (boot_cpu_has(X86_FEATURE_PCLMULQDQ)) {