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SubjectRe: [PATCH v7u1 26/31] x86: Don't enable swiotlb if there is not enough ram for it
On Tue, Jan 08, 2013 at 04:58:14PM -0800, Eric W. Biederman wrote:
> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> writes:
>
> > On Tue, Jan 08, 2013 at 03:40:11PM -0800, Yinghai Lu wrote:
> >> On Mon, Jan 7, 2013 at 7:50 PM, Yinghai Lu <yinghai@kernel.org> wrote:
> >> > On Mon, Jan 7, 2013 at 7:13 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
> >> >> I meant we should detect failure to allocate bounce buffers in in
> >> >> swiotlb_init() instead of panicing.
> >> >>
> >> >> I meant swiotlb_map_single() should either panic or simply fail.
> >> >>
> >> >> If I have read lib/swiotlb.c correctly the only place we allocate a
> >> >> bounce buffer is in swiotlb_map_single. If there are more places we can
> >> >> allocate bounce buffers those need to be handled as well.
> >> >
> >> > ok, will give it a try.
> >>
> >> please check if you are ok with attached.
> >>
> >> looks like it need more change of lines.
> >
> > The swiotlb_full check I don't believe is neccessary. You won't ever get
> > to that unless swiotlb_map_page has at least provided a bounce buffer.
> > And if the swiotlb_map_page does not have a bounce buffer it will exit
> > with:
> >
> > + if (no_iotlb_memory)
> > + return SWIOTLB_MAP_ERROR;
> > +
> >
> > which is dangerous. That is b/c there are drivers that don't use the
> > dma_mapping_error check (so check the bus address after calling
> > pci_map_*). This means they would try to do DMA on 0xffffffff (yikes!).
> >
> > That is reason the failback (v_overflow_buffer) is still in
> > usage - b/c we have drivers that might just do this and this is the last
> > resort for them. And until those drivers are fixed - we _need_ this
> > fallback to work.
>
> So instead we need to say?
>
> + if (no_iotlb_memory)
> + panic("Cannot allocate SWIOTLB buffer");


"Did not allocate SWIOTLB buffer earlier and can't now provide you with the
DMA bounce buffer."

> +
>
> Which is just making the panic a little later than it used to be and
> seems completely reasonable.

Yes. When those drivers are all fixed and then we can remove that duct-tape.


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