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SubjectRe: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use
On 08/22/2013 04:51 AM, Dave Jones wrote:
> On Wed, Aug 21, 2013 at 04:04:54PM -0700, Linus Torvalds wrote:
> > On Wed, Aug 21, 2013 at 12:03 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> > >
> > > I personally don't see bug here because
> > >
> > > - this swapped page soft dirty bit is set for non-present entries only,
> > > never for present ones, just at moment we form swap pte entry
> > >
> > > - i don't find any code which would test for this bit directly without
> > > is_swap_pte call
> >
> > Ok, having gone through the places that use swp_*soft_dirty(), I have
> > to agree. Afaik, it's only ever used on a swap-entry that has (by
> > definition) the P bit clear. So with or without Xen, I don't see how
> > it can make any difference.
> >
> > David/Konrad - did you actually see any issues, or was this just from
> > (mis)reading the code?
>
> Could this explain what I'm seeing in another thread ?
> https://lkml.org/lkml/2013/8/7/27

Was it caught with CONFIG_MEM_SOFT_DIRTY on or off? In the latter case all new
bits manipulations are no-op and couldn't cause this.

> Dave

Thanks,
Pavel


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