linux-kernel - Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use

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Date:	Wed, 21 Aug 2013 16:04:54 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Jan Beulich <JBeulich@...e.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Xen-devel@...ts.xen.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with
 existing use

On Wed, Aug 21, 2013 at 12:03 PM, Cyrill Gorcunov <gorcunov@...il.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?

                Linus
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