[Intel-gfx] [PATCH v2] mm: Track page table modifications in __apply_to_page_range()

[Chris Wilson]

Quoting Chris Wilson (2020-08-22 00:39:09)
> Quoting Andrew Morton (2020-08-21 23:34:12)
> > On Fri, 21 Aug 2020 14:37:46 +0200 Joerg Roedel <joro at 8bytes.org> wrote:
> > 
> > > The __apply_to_page_range() function is also used to change and/or
> > > allocate page-table pages in the vmalloc area of the address space.
> > > Make sure these changes get synchronized to other page-tables in the
> > > system by calling arch_sync_kernel_mappings() when necessary.
> > > 
> > > Tested-by: Chris Wilson <chris at chris-wilson.co.uk> #x86-32
> > > Cc: <stable at vger.kernel.org> # v5.8+
> > 
> > I'm trying to figure out how you figured out that this is 5.8+.  Has a
> > particular misbehaving commit been identified?
> 
> The two commits of relevance, in my eyes, were
> 
>   2ba3e6947aed ("mm/vmalloc: track which page-table levels were modified")
>   86cf69f1d893 ("x86/mm/32: implement arch_sync_kernel_mappings()")
> 
> I can reproduce the failure on v5.8, but not on v5.7. A bisect would
> seem to be plausible.

The active ingredient was

7f0a002b5a21 ("x86/mm: remove vmalloc faulting")

which explains a lot.
-Chris