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

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Message-ID: <Za/YD/0a5Mn4IOAk@e133380.arm.com>
Date: Tue, 23 Jan 2024 15:15:27 +0000
From: Dave Martin <Dave.Martin@....com>
To: Mark Brown <broonie@...nel.org>
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 05:47:55PM +0000, Mark Brown wrote:
> 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?

The sentence seemed to me to be lacking some context, but I still
haven't fully familiarised myself with the changes to the code...

If it's what you intended to write and nobody else is confused, it's
probably good.


> > 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.

I see, I guess this area needs keeping an eye on generally, but if there
are no more cases considered urgent then I guess that's fine for now
(modulo other patches in flight).

Cheers
---Dave