Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts withexisting use

[Andy Lutomirski]

On Wed, Aug 21, 2013 at 12:03 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:
> On Wed, Aug 21, 2013 at 08:50:26PM +0200, H. Peter Anvin wrote:
>> But is there a manifest bug or not?  What is the deal with Xen?
>>
>
> 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
>
> but the use of paw bit itself is confusing, so I'm working on patch which
> won't use it. Again, if someone knows where exactly access to pse bit when
> pte keeps swap entry may happen (for any purpose other than dirty page
> tracking) please share.

I doubt that there are cacheability issues here, since the swap type
already overlaps with PWT and PCD.

What happens if the page being swapped is a THP page?  (I have no idea
how, or even if, this works, but presumably PSE is important.)

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/