Date: Fri, 14 Jul 2017 02:30:54 +0100 From: Will Deacon <will.deacon@....com> To: Mark Rutland <mark.rutland@....com> Cc: ard.biesheuvel@...aro.org, kernel-hardening@...ts.openwall.com, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, akashi.takahiro@...aro.org, catalin.marinas@....com, dave.martin@....com, james.morse@....com, labbott@...oraproject.org, keescook@...omium.org Subject: Re: [RFC PATCH 1/6] arm64: use tpidr_el1 for current, free sp_el0 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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