lkml.org 
[lkml]   [2019]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings
On Tue, Oct 29, 2019 at 09:56:02AM +0100, Peter Zijlstra wrote:
> On Tue, Oct 29, 2019 at 09:43:18AM +0300, Kirill A. Shutemov wrote:
> > But some CPUs don't like to have two TLB entries for the same memory with
> > different sizes at the same time. See for instance AMD erratum 383.
> >
> > Getting it right would require making the range not present, flush TLB and
> > only then install huge page. That's what we do for userspace.
> >
> > It will not fly for the direct mapping. There is no reasonable way to
> > exclude other CPU from accessing the range while it's not present (call
> > stop_machine()? :P). Moreover, the range may contain the code that doing
> > the collapse or data required for it...
> >
> > BTW, looks like current __split_large_page() in pageattr.c is susceptible
> > to the errata. Maybe we can get away with the easy way...
>
> As you write above, there is just no way we can have a (temporary) hole
> in the direct map.
>
> We are careful about that other errata, and make sure both translations
> are identical wrt everything else.

It's not clear if it is enough to avoid the issue. "under a highly specific
and detailed set of conditions" is not very specific set of conditions :P

--
Kirill A. Shutemov

\
 
 \ /
  Last update: 2019-10-29 12:00    [W:0.109 / U:0.360 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site