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Re: [GIT PULL] x86/mm changes for v4.4

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On Sat, 07 Nov, at 08:05:54AM, Ingo Molnar wrote:
> 
> * Matt Fleming <matt@codeblueprint.co.uk> wrote:
> 
> > On Thu, 05 Nov, at 01:33:10PM, Linus Torvalds wrote:
> > > 
> > > And if this turns out to be due to EFI wanting those permissions, what should 
> > > we do? People have talked about running the EFI callbacks in their own private 
> > > page table setup, which sounds like the right idea, but until that actually 
> > > *happens*....
> > 
> > We have separate page tables today, for a few reasons, but mainly it's
> > so that we can have an identity mapping of memory present in the
> > region usually used by user processes - broken firmware still uses
> > those identity mappings even after the kernel tells it they're
> > invalid.
> > 
> > Note that when I say "separate" I'm talking about trampoline_pgd[]
> > which is also used by the x86 suspend/resume code.
> > 
> > However, turns out that the issue with the current scheme is the fact
> > that trampoline_pgd[] actually shares a couple of PGD entries with
> > swapper_pg_dir as can be seen in setup_real_mode(),
> > 
> > 
> >         trampoline_pgd = (u64 *)__va(real_mode_header->trampoline_pgd);
> >         trampoline_pgd[0] = init_level4_pgt[pgd_index(__PAGE_OFFSET)].pgd;
> >         trampoline_pgd[511] = init_level4_pgt[511].pgd;
> > 
> > 
> > So when we map the EFI regions in efi_map_regions() we're inserting
> > them into swapper_pg_dir also, which is why you're seeing the
> > warnings.
> > 
> > If I remember correctly the rationale for using trampoline_pgd[] was
> > that it already did what we wanted (provided the identity mapping) and
> > would save us the overhead of maintaining more page tables for no good
> > reason. Obviously this entire thread is a good reason.
> > 
> > I suggest we stop using trampoline_pgd[] (since it has a good reason
> > for sharing the kernel mapping PGD entries) and create our own so that
> > we can isolate EFI completely.
> 
> Ok. Could you please make this fix a priority for upcoming EFI changes?

Yep, I'll get on it.
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[GIT PULL] x86/mm changes for v4.4 Ingo Molnar <mingo@kernel.org> - 2015-11-03 12:20 +0100
  Re: [GIT PULL] x86/mm changes for v4.4 Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-04 20:30 +0100
    Re: [GIT PULL] x86/mm changes for v4.4 Dave Jones <davej@codemonkey.org.uk> - 2015-11-05 00:40 +0100
      Re: [GIT PULL] x86/mm changes for v4.4 Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-05 02:40 +0100
        Re: [GIT PULL] x86/mm changes for v4.4 Dave Jones <davej@codemonkey.org.uk> - 2015-11-05 03:20 +0100
          Re: [GIT PULL] x86/mm changes for v4.4 Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-05 22:30 +0100
            Re: [GIT PULL] x86/mm changes for v4.4 Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-05 22:40 +0100
              Re: [GIT PULL] x86/mm changes for v4.4 Matt Fleming <matt@codeblueprint.co.uk> - 2015-11-06 12:40 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Ingo Molnar <mingo@kernel.org> - 2015-11-07 08:10 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Matt Fleming <matt@codeblueprint.co.uk> - 2015-11-07 11:10 +0100
            Re: [GIT PULL] x86/mm changes for v4.4 Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-05 23:10 +0100
              Re: [GIT PULL] x86/mm changes for v4.4 Borislav Petkov <bp@alien8.de> - 2015-11-05 23:30 +0100
            Re: [GIT PULL] x86/mm changes for v4.4 Ingo Molnar <mingo@kernel.org> - 2015-11-06 08:00 +0100
              Re: [GIT PULL] x86/mm changes for v4.4 Andy Lutomirski <luto@amacapital.net> - 2015-11-06 08:10 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Matt Fleming <matt@codeblueprint.co.uk> - 2015-11-06 14:10 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Borislav Petkov <bp@alien8.de> - 2015-11-06 14:30 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Ingo Molnar <mingo@kernel.org> - 2015-11-07 08:10 +0100
              Re: [GIT PULL] x86/mm changes for v4.4 Ingo Molnar <mingo@kernel.org> - 2015-11-06 08:50 +0100
              Re: [GIT PULL] x86/mm changes for v4.4 Matt Fleming <matt@codeblueprint.co.uk> - 2015-11-06 13:40 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Ingo Molnar <mingo@kernel.org> - 2015-11-07 08:10 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-11-07 08:40 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Kees Cook <keescook@chromium.org> - 2015-11-08 08:00 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-11-08 09:00 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Kees Cook <keescook@chromium.org> - 2015-11-09 22:10 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-11-10 08:10 +0100
                Re: [GIT PULL] x86/mm changes for v4.4 Kees Cook <keescook@chromium.org> - 2015-11-10 21:20 +0100

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