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

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Message-ID: <20220910053203.GB23052@lst.de>
Date:   Sat, 10 Sep 2022 07:32:03 +0200
From:   Christoph Hellwig <hch@....de>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     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>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Rafael Antognolli <Rafael.Antognolli@...el.com>,
        Scott Bauer <scott.bauer@...el.com>,
        Serge Semin <fancer.lancer@...il.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

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.