lkml.org 
[lkml]   [2014]   [Dec]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] iommu/vt-d: Fix an off-by-one bug in __domain_mapping()
On Tue, Dec 02, 2014 at 10:34:35AM +0000, David Woodhouse wrote:
> __domain_mapping() is an amalgamation of the old domain_pfn_mapping()
> and domain_sg_mapping() functions. When I did that, in commit 9051aa026,
> the 'sg_res' variable was used *only* for tracking how many pages were
> left in the current scatterlist element, before we had to get the next
> one from the sglist.
>
> For reasons which are lost now, in the case of a simple pfn range I was
> setting 'sg_res = nr_pages + 1' to ensure that we *never* got down to
> sg_res=0 and tried to look for more from the (non-existent, in this
> case) sglist.
>
> Later in commit 6dd9a7c73 we added large page support, using sg_res in a
> way which actually required it to be accurate. And now we have an
> off-by-one because we'll actually *try* to use a 2GiB large page for a
> mapping of size 0x1ff000, because of that '+1'.
>
> The BUG_ON is entirely correct here, and correctly highlighted the
> problem.
>
> However, the +1 is no longer necessary, because the check that needed it
> was also modified to read 'if (sg_res && nr_pages)', which is perfectly
> sufficient and arguably how it should have been done in the first place.
>
> I had an almost identical patch last week for internal testing, because
> I stupidly hadn't noticed that Jiang had beaten me to it.
>
> Acked-By: David Woodhouse <David.Woodhouse@intel.com>
>
> > > This issue was introduced in v2.6.31, but intel-iommu.c has
> > > been moved into drivers/iommu in v3.1. So what's the preferred way
> > > to deal with stable kernels between v2.6.31 and v3.1?
> >
> > Just remove the kernel version marker from the stable tag. The stable
> > kernel maintainers for kernels >3.1 will ask you to backport the patch
> > or just backport it by themselfes.
>
> I think this is only an issue since commit 6dd9a7c737 added super page
> support in 3.0, isn't it? Before that, the +1 was *needed*.

Okay guys, thanks for the explanations. I applied the patch to the
x86/vt-d branch and changed the stable tag to >= 3.0.


Joerg



\
 
 \ /
  Last update: 2014-12-02 13:41    [W:0.045 / U:0.420 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site