linux-kernel - Re: [PATCH 1/2] arm64: entry: remove pointless SPSR mode check

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Message-ID: <20160106121524.GL6301@e104818-lin.cambridge.arm.com>
Date:	Wed, 6 Jan 2016 12:15:25 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	cmetcalf@...hip.com, will.deacon@....com,
	linux-kernel@...r.kernel.org, luto@...capital.net,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] arm64: entry: remove pointless SPSR mode check

On Tue, Jan 05, 2016 at 05:33:34PM +0000, Mark Rutland wrote:
> In work_pending  we may skip work if the stacked SPSR value represents
> anything other than an EL0 context. We then immediately invoke the
> kernel_exit 0 macro as part of ret_to_user, assuming a return to EL0.
> This is somewhat confusing.
> 
> We use work_pending as part of the ret_to_user/ret_fast_syscall state
> machine. We only use ret_fast_syscall in the return from an SVC issued
> from EL0. We use ret_to_user for return from EL0 exception handlers and
> also for return from ret_from_fork in the case the task was not a kernel
> thread (i.e. it is a user task).
> 
> Thus in all cases the stacked SPSR value must represent an EL0 context,
> and the check is redundant. This patch removes it, along with the now
> unused no_work_pending label.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Chris Metcalf <cmetcalf@...hip.com>
> Cc: Will Deacon <will.deacon@....com>

Acked-by: Catalin Marinas <catalin.marinas@....com>
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