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Re: [RFC PATCH 1/6] arm64: use tpidr_el1 for current, free sp_el0

From Will Deacon <will.deacon@arm.com>
Newsgroups linux.kernel
Subject Re: [RFC PATCH 1/6] arm64: use tpidr_el1 for current, free sp_el0
Date 2017-07-14 03:40 +0200
Message-ID <u2XKi-4Ps-3@gated-at.bofh.it> (permalink)
References <u2ysy-5Ke-5@gated-at.bofh.it> <u2ysy-5Ke-17@gated-at.bofh.it>
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On Wed, Jul 12, 2017 at 11:32:58PM +0100, Mark Rutland wrote:
> Today we use TPIDR_EL1 for our percpu offset, and SP_EL0 for current
> (and current::thread_info, which is at offset 0).
> 
> Using SP_EL0 in this way prevents us from using EL1 thread mode, where
> SP_EL0 is not addressable (since it's used as the active SP). It also
> means we can't use SP_EL0 for other purposes (e.g. as a
> scratch-register).
> 
> This patch frees up SP_EL0 for such usage, by storing the percpu offset
> in current::thread_info, and using TPIDR_EL1 to store current. As we no
> longer need to update SP_EL0 at EL0 exception boundaries, this allows us
> to delete some code.

Does this mean we can just use asm-generic/percpu.h?

Will

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[RFC PATCH 0/6] arm64: alternative VMAP_STACK implementation Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
  [RFC PATCH 5/6] arm64: keep track of current stack Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
  [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
    Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-13 09:00 +0200
      Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-13 13:00 +0200
        Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-13 13:50 +0200
          Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-13 18:20 +0200
            Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-13 20:00 +0200
              Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-13 20:30 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-14 12:40 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-14 12:50 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-14 14:30 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-14 16:10 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-14 16:20 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Robin Murphy <robin.murphy@arm.com> - 2017-07-14 16:40 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Robin Murphy <robin.murphy@arm.com> - 2017-07-14 17:10 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-14 17:20 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-14 17:30 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-14 23:30 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-16 02:10 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Mark Rutland <mark.rutland@arm.com> - 2017-07-14 15:00 +0200
                Re: [kernel-hardening] Re: [RFC PATCH 6/6] arm64: add VMAP_STACK and  detect out-of-bounds SP Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-14 15:00 +0200
  [RFC PATCH 4/6] arm64: pass stack base to secondary_start_kernel Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
  [RFC PATCH 1/6] arm64: use tpidr_el1 for current, free sp_el0 Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
    Re: [RFC PATCH 1/6] arm64: use tpidr_el1 for current, free sp_el0 Will Deacon <will.deacon@arm.com> - 2017-07-14 03:40 +0200
  [RFC PATCH 3/6] arm64: pad stacks to PAGE_SIZE for VMAP_STACK Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
  [RFC PATCH 2/6] arm64: avoid open-coding THREAD_SIZE{,_ORDER} Mark Rutland <mark.rutland@arm.com> - 2017-07-13 00:40 +0200
    Re: [RFC PATCH 2/6] arm64: avoid open-coding THREAD_SIZE{,_ORDER} James Morse <james.morse@arm.com> - 2017-07-13 12:20 +0200
      Re: [RFC PATCH 2/6] arm64: avoid open-coding THREAD_SIZE{,_ORDER} Mark Rutland <mark.rutland@arm.com> - 2017-07-13 13:30 +0200

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