linux-kernel - Re: [PATCH 1/2] ARCv2: LIB: memeset: fix doing prefetchw outside of buffer

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Message-ID: <C2D7FE5348E1B147BCA15975FBA23075014642748E@US01WEMBX2.internal.synopsys.com>
Date:   Tue, 15 Jan 2019 16:58:17 +0000
From:   Vineet Gupta <vineet.gupta1@...opsys.com>
To:     Eugeniy Paltsev <eugeniy.paltsev@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexey Brodkin" <alexey.brodkin@...opsys.com>
Subject: Re: [PATCH 1/2] ARCv2: LIB: memeset: fix doing prefetchw outside of
 buffer

On 1/15/19 4:00 AM, Eugeniy Paltsev wrote:
>>> -#ifdef PREALLOC_NOT_AVAIL
>>> -	prefetchw [r3, 64]	;Prefetch the next write location
>>> -#else
>>> -	prealloc  [r3, 64]
>>> -#endif
>>> +	PREALLOC_INSTR([r3, 64]) ;Prefetch the next write location
>> These are not solving the issue - I'd break this up and move these bits to your
>> next patch.
> Actually these are solving another issue - current implementation may call
> 'prealloc' instruction for L1 cache line which doesn't fully belongs to
> memeset area in case of 128B L1 D$ line length. As the 'prealloc' fill cache line
> with zeros this leads to data corruption.
>
> So I would better keep these changes in this 'fix' patch.

Fair enough. Although technically it is different bug which we haven't actually
hit, found by code review.

> BTW, I've forgot again to add Cc: stable@...r.kernel.org, could you add it for me,
> when applying patch?
> Thanks.

Yes, I did that already !

-Vineet