lkml.org 
[lkml]   [2019]   [Sep]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared
On Fri, Sep 06, 2019 at 07:57:42AM -0700, Matthew Wilcox wrote:
> On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote:
> > * This really shouldn't fail, because the page is there
> > * in the page tables. But it might just be unreadable,
> > * in which case we just give up and fill the result with
> > - * zeroes.
> > + * zeroes. If PTE_AF is cleared on arm64, it might
> > + * cause double page fault. So makes pte young here
>
> How about:
> * zeroes. On architectures with software "accessed" bits,
> * we would take a double page fault here, so mark it
> * accessed here.
>
> > */
> > + if (!pte_young(vmf->orig_pte)) {
>
> Let's guard this with:
>
> if (arch_sw_access_bit && !pte_young(vmf->orig_pte)) {
>
> #define arch_sw_access_bit 0
> by default and have arm64 override it (either to a variable or a constant
> ... your choice). Also, please somebody decide on a better name than
> arch_sw_access_bit.

I'm not good at names either (is arch_faults_on_old_pte any better?) but
I'd make this a 0 args call: arch_sw_access_bit(). This way we can make
it a static inline function on arm64 with some static label check.

--
Catalin

\
 
 \ /
  Last update: 2019-09-10 11:16    [W:0.051 / U:3.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site