linux-kernel - Re: [PATCH 2/2] block: sed-opal: Cache-line-align the cmd/resp buffers

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Date:   Sun, 11 Sep 2022 19:28:54 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Jonathan Derrick <jonathan.derrick@...el.com>,
        Revanth Rajashekar <revanth.rajashekar@...el.com>,
        Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
        Jens Axboe <axboe@...com>, Sagi Grimberg <sagi@...mberg.me>,
        Rafael Antognolli <Rafael.Antognolli@...el.com>,
        Scott Bauer <scott.bauer@...el.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] block: sed-opal: Cache-line-align the cmd/resp
 buffers

Hello Christoph

On Sat, Sep 10, 2022 at 07:32:03AM +0200, Christoph Hellwig wrote:
> On Fri, Sep 09, 2022 at 10:19:16PM +0300, Serge Semin wrote:
> > In accordance with [1] the DMA-able memory buffers must be
> > cacheline-aligned otherwise the cache writing-back and invalidation
> > performed during the mapping may cause the adjacent data being lost. It's
> > specifically required for the DMA-noncoherent platforms. Seeing the
> > opal_dev.{cmd,resp} buffers are used for DMAs in the NVME and SCSI/SD
> > drivers in framework of the nvme_sec_submit() and sd_sec_submit() methods
> > respectively we must make sure the passed buffers are cacheline-aligned to
> > prevent the denoted problem.
>
 
> Same comment as for the previous one, this should work, but I think
> separate allocations for the DMAable buffers would document the intent
> much better.  Given that the opal initialization isn't a fast path
> I don't think that the overhead should matter either.

Thanks for the comment. I see your point. Let's hear the subsystem
maintainers out for their opinion regarding the most suitable solution
in this case. If they get to agree with you I'll resend the series
with altered fixes.

-Sergey