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

Serge Semin
2022-09-25T22:31:00Z

@Jens, @Revanth, @Jonathan do you have anything to say regarding the
patch and what @Christoph suggested?

On Sun, Sep 11, 2022 at 07:28:57PM +0300, Serge Semin wrote:
> 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