lkml.org 
[lkml]   [2008]   [Sep]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/3] fix GART to respect device's dma_mask about virtual mappings
On Tue, Sep 16, 2008 at 05:52:11PM +0200, Joerg Roedel wrote:
> On Tue, Sep 16, 2008 at 10:20:40PM +0900, FUJITA Tomonori wrote:
> > On Tue, 16 Sep 2008 02:54:32 +0200
> > Andi Kleen <andi@firstfloor.org> wrote:
> >
> > > FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> writes:
> > >
> > > > Currently, gart IOMMU ignores device's dma_mask when it does virtual
> > > > mappings. So it could give a device a virtual address that the device
> > > > can't access to.
> > >
> > > Huh? That is what the need_iommu() logic in gart_map_sg()
> > > does. An I'm not aware of any bugs in this area.
> >
> > What the need_iommu() does is seeing if GART needs to do virtual
> > mappings or not.
> >
> > (After need_iommu() checking) What this patchset does is to guarantee
> > that GART provides a virtual address that a device can access to.
> >
> >
> > > Did you actually see that failure in practice? I don't see
> > > how it could happen.
> >
> > No, I did not. This patchset does the right thing theoretically, I
> > think, but if such problem never happens for GART, I'll drop the patch
> > for GART. Joerg?
>
> I am not aware of any failures which are fixed by these patches.

AFAIK all subsystems deal with it on their own. That is because i386
is the same (no remapping pci_map_* at all) and subsystems are usually
written to i386 semantics.

> But in
> theory there could be failures.

They will stay failures because GFP_DMA bouncing can not be really
done today in the pci_map_* layer. With a lot of effort you could
probably fix all that, but I doubt it would be worth the effort for
the few devices left with DMA masks < 32bit.

-Andi

>
> Joerg
>
> --
> | AMD Saxony Limited Liability Company & Co. KG
> Operating | Wilschdorfer Landstr. 101, 01109 Dresden, Germany
> System | Register Court Dresden: HRA 4896
> Research | General Partner authorized to represent:
> Center | AMD Saxony LLC (Wilmington, Delaware, US)
> | General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy
>

--
ak@linux.intel.com


\
 
 \ /
  Last update: 2008-09-16 18:19    [W:0.066 / U:0.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site