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    SubjectRe: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver
    On Fri, Jul 13 2007, Geert Uytterhoeven wrote:
    > On Fri, 13 Jul 2007, Jens Axboe wrote:
    > > On Fri, Jul 13 2007, 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
    > > >
    > > > flush_kernel_dcache_page(kaddr)
    > > >
    > > > before doing the kunmap.
    > > >
    > > > Otherwise it looks OK from the SCSI point of view.
    >
    > kmap() just returns page_address() on ppc64, as there's no highmem.
    > kunmap() is a no-op.
    >
    > So technically I could just use page_address() directly, but Christoph wanted
    > me to keep the kmap()/kunmap() sequence because it's considered a good
    > practice.

    If you have the kmap sequence there, put the flush in as well. People
    copy code, you know... Or put a big comment explaining why it isn't
    needed.

    > > Well, even worse is that fact that it's using KM_USER0 from interrupt
    > > context.
    >
    > So should I replace it by e.g. KM_IRQ0?
    > I'm not so familiar with these parts, and I couldn't find what these values
    > really mean.

    You corrupt data, using KM_USER0 from interrupt context. So it's a big
    flaw right now. Use KM_IRQ0 for code where interrupts are always
    disabled.

    --
    Jens Axboe

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