linux-kernel - Re: [PATCH] arm64/signal: Don't assume that TIF

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Message-ID: <Zaq1y9XpmzTsXDp8@finisterre.sirena.org.uk>
Date: Fri, 19 Jan 2024 17:47:55 +0000
From: Mark Brown <broonie@...nel.org>
To: Dave Martin <Dave.Martin@....com>
Cc: Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <will@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] arm64/signal: Don't assume that TIF_SVE means we saved
 SVE state

On Fri, Jan 19, 2024 at 04:31:13PM +0000, Dave Martin wrote:
> On Fri, Jan 19, 2024 at 12:29:13PM +0000, Mark Brown wrote:

> > When we are in a syscall we will only save the FPSIMD subset even though
> > the task still has access to the full register set, and on context switch

> (Pedantic nit: "A even if B" (= "A applies even in that subset of cases
> where B"), instead of "A even though B" (= "A applies notwithstanding
> that it is always the case that B") (?)  If the SVE trapping were
> ripped out altogether, it would be a different and rather simpler
> story...)

I really can't follow what you're trying to say here.  I'm not sure I
where the bit about "always" comes from here?

> If the historical meanings of TIF_SVE have been split up (which seems a
> good idea), does that resolve all of the "bare"
> test_thread_flag(TIF_SVE) that were still there?

There's a couple more, but this is all of them in the signal handling
code - I should have one or two more patches.  Most of the usage is
actually checking the trapping and therefore fine.

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