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Date:	Fri, 19 Sep 2014 15:19:24 -0700
From:	Filipe Brandenburger <>
To:	Andy Lutomirski <>
Cc:	"H. Peter Anvin" <>, Greg Thelen <>,
	X86 ML <>, Thomas Gleixner <>,
	Michael Davidson <>,
	Ingo Molnar <>,
	Richard Larocque <>,
	"" <>,
	Linux API <>
Subject: Re: [PATCH] x86/vdso: Add prctl to set per-process VDSO load


On Fri, Sep 19, 2014 at 3:09 PM, Andy Lutomirski <> wrote:
> On Fri, Sep 19, 2014 at 3:02 PM, Filipe Brandenburger <> wrote:
>> In case that's useful, I was looking at swapping the vvar page by
>> changing the vm_special_mapping to change the pages array between the
>> actual vvar page and the zero page and using zap_page_range to force
>> the next access to go through a page fault that would remap it.
> That will do it globally, since the vm_special_mapping is global.  I
> was just thinking of using remap_pfn_range.

Sorry if I wasn't clear... That's the exact point of my patch, to make
vm_special_mapping local to the task.

I started with an approach of keeping a struct vm_special_mapping + a
struct page * array per mm_struct.

I was also looking at keeping two static vm_special_mapping structs,
one with the actual vvar page and the other with the zero page and
then swapping vma->vm_private_data to point to the appropriate one.

> Give me another day or two to straighten out the vma stuff, although
> it shouldn't impact your patches too much.  The main effect will be
> that you'll be able to rely on mm->context.vdso (renamed to
> vvar_vma_start, most likey) being correct.  Currently, you should
> *not* rely on it, especially if CRIU is involved.

Cool! As I said, let me know if you'd like to see some of my
incomplete patches or if you'd like me to keep working on them to show
you something more complete.

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