Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 19 Sep 2014 15:31:40 -0700 | Subject | Re: [PATCH] x86/vdso: Add prctl to set per-process VDSO load |
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On Fri, Sep 19, 2014 at 3:19 PM, Filipe Brandenburger <filbranden@google.com> wrote: > Hi, > > On Fri, Sep 19, 2014 at 3:09 PM, Andy Lutomirski <luto@amacapital.net> wrote: >> On Fri, Sep 19, 2014 at 3:02 PM, Filipe Brandenburger <filbranden@google.com> 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.
This sounds like it may be more complicated than necessary. Is there any reason that just doing remap_pfn_range on the vvar page isn't enough?
Changing out the text is a whole can of worms involving self-modifying code, although it may be completely safe if done through the page tables. But I don't think you can't use remap_pfn_range for that.
> >> 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.
Maybe better: what exactly are you trying to do?
--Andy
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