Re: [Xen-devel] Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use

[Pavel Emelyanov <xemul@xxxxxxxxxxxxx>]

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@xxxxxxxxx> 
> 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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