linux-kernel - Re: [PATCH v5 2/2] arm64: enable context tracking

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Message-ID: <20140528114438.GF15222@arm.com>
Date:	Wed, 28 May 2014 12:44:38 +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 v5 2/2] arm64: enable context tracking

Hi Larry,

On Mon, May 26, 2014 at 07:56:13PM +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 and all of the "error" paths).
> 
> 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).
> 
> The calls to ct_user_exit are made after hw debugging has been
> enabled (enable_dbg_and_irq).
> 
> The call to ct_user_enter is made at the beginning of the
> kernel_exit macro.
> 
> This patch is based on earlier work by Kevin Hilman.
> Save/restore optimizations were also done by Kevin.

Apologies if we've discussed this before (it rings a bell), but why are we
penalising the fast syscall path with this? Shouldn't TIF_NOHZ contribute to
out _TIF_WORK_MASK, then we could do the tracking on the syscall slow path?

I think that would tidy up your mov into x19 too.

Also -- how do you track ret_from_fork in the child with these patches?

Will
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