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

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Message-ID: <20201211130058.GZ2414@hirez.programming.kicks-ass.net>
Date:   Fri, 11 Dec 2020 14:00:58 +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, thomas.lendacky@....com
Subject: Re: [PATCH] crypto: x86/crc32c-intel - Don't match some Zhaoxin CPUs

On Fri, Dec 11, 2020 at 07:29:04PM +0800, Tony W Wang-oc wrote:
> The driver crc32c-intel match CPUs supporting X86_FEATURE_XMM4_2.
> On platforms with Zhaoxin CPUs supporting this X86 feature, When
> crc32c-intel and crc32c-generic are both registered, system will
> use crc32c-intel because its .cra_priority is greater than
> crc32c-generic. This case expect to use crc32c-generic driver for
> some Zhaoxin CPUs to get performance gain, So remove these Zhaoxin
> CPUs support from crc32c-intel.
> 
> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@...oxin.com>
> ---
>  arch/x86/crypto/crc32c-intel_glue.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/crypto/crc32c-intel_glue.c b/arch/x86/crypto/crc32c-intel_glue.c
> index feccb52..6dafdae 100644
> --- a/arch/x86/crypto/crc32c-intel_glue.c
> +++ b/arch/x86/crypto/crc32c-intel_glue.c
> @@ -222,8 +222,16 @@ MODULE_DEVICE_TABLE(x86cpu, crc32c_cpu_id);
>  
>  static int __init crc32c_intel_mod_init(void)
>  {
> +	struct cpuinfo_x86 *c = &boot_cpu_data;
> +
>  	if (!x86_match_cpu(crc32c_cpu_id))
>  		return -ENODEV;
> +
> +	if (c->x86_vendor == X86_VENDOR_ZHAOXIN || c->x86_vendor == X86_VENDOR_CENTAUR) {
> +		if (c->x86 == 0x6 || (c->x86 == 0x7 && c->x86_model <= 0x3b))
> +			return -ENODEV;
> +	}

Egads, why can't you use that x86_match_cpu() above, and also this
really wants a comment on why you're excluding these chips. Also, since
(IIRC) ZHAOXIN is basically AND, shouldn't they also be listed?

That is; write it like:

	m = x86_match_cpu(crc32_cpu_id);
	if (!m || !m->data)
		return -ENODEV;

That way you can have positive and negative matches in the array
(obviously the existing FEATURE test would need data=1 and be last).