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Date: Fri, 15 May 2015 12:39:05 +0300 From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru> To: Mark Williamson <mwilliamson@...o-software.com> CC: linux-mm@...ck.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>, kernel list <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Pavel Emelyanov <xemul@...allels.com>, Linux API <linux-api@...r.kernel.org>, Andy Lutomirski <luto@...capital.net>, Vlastimil Babka <vbabka@...e.cz>, Pavel Machek <pavel@....cz>, Mark Seaborn <mseaborn@...omium.org>, "Kirill A. Shutemov" <kirill@...temov.name>, Linus Torvalds <torvalds@...ux-foundation.org>, Daniel James <djames@...o-software.com>, Finn Grimwood <fgrimwood@...o-software.com> Subject: Re: [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages mapped only here On 14.05.2015 21:50, Mark Williamson wrote: > Hi Konstantin, > > On Wed, May 13, 2015 at 11:51 AM, Konstantin Khlebnikov > <khlebnikov@...dex-team.ru> wrote: >> On 12.05.2015 15:05, Mark Williamson wrote: > <snip> >>> 1. I was hoping we'd be able to backport a compatible fix to older >>> kernels that might adopt the pagemap permissions change. Using the V2 >>> format flags rules out doing this for kernels that are too old to have >>> soft-dirty, I think. >>> >>> 2. From our software's PoV, I feel it's worth noting that it doesn't >>> strictly fix ABI compatibility, though I realise that's probably not >>> your primary concern here. We'll need to modify our code to write the >>> clear_refs file but that change is OK for us if it's the preferred >>> solution. > <snip> >> I prefer to backport v2 format (except soft-dirty bit and clear_refs) >> into older kernels. Page-shift bits are barely used so nobody will see >> the difference. > > My concern was whether a change to format would be acceptable to > include in the various -stable kernels; they are already including the > additional protections on pagemap, so we're starting to need our > fallback mode in distributions. Do you think that such a patch would > be acceptable there? > > (As an application vendor we're likely to be particularly stuck with > what the commercial distributions decide to ship, which is why I'm > trying to keep an eye on this) > > I appreciate that this is a slightly administrative concern! I > definitely like the technical approach of this code and it seems to > work fine for us. I cannot guarantee that v2 format will be accepted into stable kernels and into distributives. I'm not the gate keeper. As a fallback probably you should invent some kind of suid helper which gives you access to required information without exposing pfn. For example: it gets pids and memory ranges as arguments and prints bitmap of CoWed pages into stdout. -- Konstantin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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