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Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3

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On Wed, Aug 16, 2017 at 09:14:41AM -0700, Andy Lutomirski wrote:
> On Wed, Aug 16, 2017 at 5:57 AM, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> > On Wed, 16 Aug, at 12:03:22PM, Mark Rutland wrote:
> >>
> >> I'd expect we'd abort at a higher level, not taking any sample. i.e.
> >> we'd have the core overflow handler check in_funny_mm(), and if so, skip
> >> the sample, as with the skid case.
> >
> > FYI, this is my preferred solution for x86 too.
> 
> One option for the "funny mm" flag would be literally the condition
> current->mm != current->active_mm.  I *think* this gets all the cases
> right as long as efi_switch_mm is careful with its ordering and that
> the arch switch_mm() code can handle the resulting ordering.  (x86's
> can now, I think, or at least will be able to in 4.14 -- not sure
> about other arches).

For arm64 we'd have to rework things a bit to get the ordering right
(especially when we flip to/from the idmap), but otherwise this sounds sane to
me.

> That being said, there's a totally different solution: run EFI
> callbacks in a kernel thread.  This has other benefits: we could run
> those callbacks in user mode some day, and doing *that* in a user
> thread seems like a mistake.

I think that wouldn't work for CPU-bound perf events (which are not
ctx-switched with the task).

It might be desireable to do that anyway, though.

Thanks,
Mark.

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[PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3 Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> - 2017-08-15 21:30 +0200
  Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Andy Lutomirski <luto@kernel.org> - 2017-08-15 23:50 +0200
    Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> - 2017-08-16 02:30 +0200
      Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Andy Lutomirski <luto@kernel.org> - 2017-08-16 02:50 +0200
    Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-08-16 11:40 +0200
      Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Mark Rutland <mark.rutland@arm.com> - 2017-08-16 12:00 +0200
        Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Will Deacon <will.deacon@arm.com> - 2017-08-16 12:10 +0200
          Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Mark Rutland <mark.rutland@arm.com> - 2017-08-16 13:10 +0200
            Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Matt Fleming <matt@codeblueprint.co.uk> - 2017-08-16 15:00 +0200
              Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Andy Lutomirski <luto@kernel.org> - 2017-08-16 18:20 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Mark Rutland <mark.rutland@arm.com> - 2017-08-16 19:20 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Will Deacon <will.deacon@arm.com> - 2017-08-17 12:40 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Andy Lutomirski <luto@kernel.org> - 2017-08-17 18:00 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Peter Zijlstra <peterz@infradead.org> - 2017-08-21 12:40 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3 Andy Lutomirski <luto@amacapital.net> - 2017-08-21 16:00 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Peter Zijlstra <peterz@infradead.org> - 2017-08-21 16:20 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3 Andy Lutomirski <luto@amacapital.net> - 2017-08-21 17:30 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Peter Zijlstra <peterz@infradead.org> - 2017-08-21 18:00 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-08-21 18:10 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> - 2017-08-24 01:00 +0200
                Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Peter Zijlstra <peterz@infradead.org> - 2017-08-21 19:30 +0200
    Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually  twiddling with cr3 Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> - 2017-08-25 04:50 +0200

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