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From: Catalin Marinas <catalin.marinas@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>, Julien Grall <julien@xen.org>,
	Zhang Lei <zhang.lei@jp.fujitsu.com>,
	Dave Martin <Dave.Martin@arm.com>,
	Daniel Kiss <Daniel.Kiss@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64/sve: Rework SVE access trap to convert state in registers
Date: Thu, 8 Apr 2021 17:43:27 +0100	[thread overview]
Message-ID: <20210408164327.GB7676@arm.com> (raw)
In-Reply-To: <20210407124806.GC5510@sirena.org.uk>

On Wed, Apr 07, 2021 at 01:48:06PM +0100, Mark Brown wrote:
> On Wed, Apr 07, 2021 at 12:45:12PM +0100, Catalin Marinas wrote:
> > The other case is TIF_FOREIGN_FPSTATE being set in do_sve_acc(). Since
> > we never return to user with this flag set, when can we actually hit the
> > 'else' path in your patch?
> 
> We'd have to have been preempted between entering the kernel and
> actually handling the access trap, I can't think of a scenario where
> that would happen but it seemed easier to have the code to handle it
> than to make absolutely sure that there was no possible case that I was
> missing.  I think we should have the detection code either way in case
> it does end up happening somehow but it could be changed to use
> WARN_ON_ONCE() or something instead of silently handling it?

If we get preempted before do_sve_acc() (and that's possible as the
interrupts are enabled), if the interrupted thread wakes up on another
CPU it will have TIF_FOREIGN_FPSTATE set so that it retrieves the new
state.

So the patch looks fine to me.

-- 
Catalin

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  parent reply	other threads:[~2021-04-08 16:45 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-12 19:03 [PATCH] arm64/sve: Rework SVE access trap to convert state in registers Mark Brown
2021-04-07 11:45 ` Catalin Marinas
2021-04-07 12:48   ` Mark Brown
2021-04-07 15:55     ` Mark Brown
2021-04-08 16:43     ` Catalin Marinas [this message]
2021-04-08 18:00 ` Catalin Marinas

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