From: Mark Brown <broonie@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Shuah Khan <shuah@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v2] kselftest/arm64: Exit streaming mode after collecting signal context
Date: Thu, 20 Jul 2023 12:35:02 +0100 [thread overview]
Message-ID: <037425cc-bf17-4dfd-8bdc-c1c10b153ebb@sirena.org.uk> (raw)
In-Reply-To: <20230720103113.GA11034@willie-the-truck>
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On Thu, Jul 20, 2023 at 11:31:13AM +0100, Will Deacon wrote:
> On Wed, Jul 12, 2023 at 12:02:30PM +0100, Mark Brown wrote:
> > + /*
> > + * This is a memset() but we don't want the compiler to
> > + * optimise it into either instructions or a library call
> > + * which might be incompatible with streaming mode.
> > + */
> > + for (i = 0; i < td->live_sz; i++) {
> > + asm volatile("nop"
> > + : "+m" (*dest_uc)
> > + :
> > + : "memory");
> I don't think it's save to use "+m" here, since the compiler can assume
> that the address is used exactly once in the asm. If a post-indexed
> addressing mode is generated, then you can end up with register corruption.
> Stepping back, why not use either barrier() or OPTIMIZER_HIDE_VAR()
> instead?
That should work. I was mostly just open coding OPTIMIZER_HIDE_VAR()
and noticed that memory constraints were a thing.
> The most robust fix would be to write all of the streaming mode code in
> asm, but I can appreciate that's a tonne of work for a testcase.
It's probably more proportionate to add a dependency on toolchain
support for SME, but that'd mean we hardly ever run the tests.
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prev parent reply other threads:[~2023-07-20 11:35 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-12 11:02 [PATCH v2] kselftest/arm64: Exit streaming mode after collecting signal context Mark Brown
2023-07-20 10:31 ` Will Deacon
2023-07-20 11:35 ` Mark Brown [this message]
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