linux-kernel - Re: [PATCH v2 2/2] arm64: enable context tracking

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Date:	Wed, 7 May 2014 11:17:09 +0100
From:	Will Deacon <will.deacon@....com>
To:	Larry Bassel <larry.bassel@...aro.org>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"khilman@...aro.org" <khilman@...aro.org>
Subject: Re: [PATCH v2 2/2] arm64: enable context tracking

On Wed, May 07, 2014 at 12:32:29AM +0100, Larry Bassel wrote:
> Make calls to ct_user_enter when the kernel is exited
> and ct_user_exit when the kernel is entered (in el0_da,
> el0_ia, el0_svc, el0_irq).

Why only these entry points? I can reschedule after any exception from EL0,
so I'd expect all exceptions from userspace to need annotating, no?

> These macros expand to function calls which will only work
> properly if el0_sync and related code has been rearranged
> (in a previous patch of this series).
> 
> In order to avoid saving registers, the slow syscall path
> is forced (as x86 does).

... and if you decide to handle undef exceptions, I think you'll need
the register saving too, in case the kernel needs to perform emulation.

Will
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