linux-kernel - Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

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Date:	Sat, 14 Jul 2007 09:06:10 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	James Bottomley <James.Bottomley@...elEye.com>
Cc:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	Jens Axboe <axboe@...nel.dk>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alessandro Rubini <rubini@...ion.unipv.it>,
	linuxppc-dev@...abs.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

On Fri, 2007-07-13 at 09:02 -0400, James Bottomley wrote:
> On Wed, 2007-07-04 at 15:22 +0200, Geert Uytterhoeven wrote:
> > +                       kaddr = kmap_atomic(sgpnt->page, KM_USER0);
> > +                       if (!kaddr)
> > +                               return -1;
> > +                       len = sgpnt->length;
> > +                       if ((req_len + len) > buflen) {
> > +                               active = 0;
> > +                               len = buflen - req_len;
> > +                       }
> > +                       memcpy(kaddr + sgpnt->offset, buf + req_len,
> > len);
> > +                       kunmap_atomic(kaddr, KM_USER0);
> 
> This isn't a SCSI objection, but this sequence appears several times in
> this driver.  It's wrong for a non-PIPT architecture (and I believe the
> PS3 is VIPT) because you copy into the kernel alias for the page, which
> dirties the line in the cache of that alias (the user alias cache line
> was already invalidated).  However, unless you flush the kernel alias to
> main memory, the user could read stale data.  The way this is supposed
> to be done is to do a 

Nah, we have no cache aliasing on ppc, at least not that matter here and
not on cell.

Ben.

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