Re: [RFC/RFT PATCH 01/16] arm64: cpufeature: Detect SSBS and advertise to userspace

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Jeremy Linton <jeremy.linton@arm.com>,
	Andre Przywara <andre.przywara@arm.com>,
	Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC/RFT PATCH 01/16] arm64: cpufeature: Detect SSBS and advertise to userspace
Date: Tue, 8 Oct 2019 16:39:02 +0200	[thread overview]
Message-ID: <CAKv+Gu-rPLhsnEuZUPXrcfXaBjbK4Sfam+1k_-ioZ95-+vQKLw@mail.gmail.com> (raw)
In-Reply-To: <20191008143537.GA14523@lakrids.cambridge.arm.com>

On Tue, 8 Oct 2019 at 16:35, Mark Rutland <mark.rutland@arm.com> wrote:
>
> Hi Ard,
>
> I have a few general backport notes below, and one issue with this
> patch/series.
>
> On Fri, Oct 04, 2019 at 02:04:15PM +0200, Ard Biesheuvel wrote:
> > From: Will Deacon <will.deacon@arm.com>
> >
> > Armv8.5 introduces a new PSTATE bit known as Speculative Store Bypass
> > Safe (SSBS) which can be used as a mitigation against Spectre variant 4.
> >
> > Additionally, a CPU may provide instructions to manipulate PSTATE.SSBS
> > directly, so that userspace can toggle the SSBS control without trapping
> > to the kernel.
> >
> > This patch probes for the existence of SSBS and advertise the new instructions
> > to userspace if they exist.
> >
> > Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > (cherry picked from commit d71be2b6c0e19180b5f80a6d42039cc074a693a2)
>
> This should be the first line, formatted like:
>
> commit d71be2b6c0e19180b5f80a6d42039cc074a693a2 upstream.
>
> ... as documented in Documentation/process/stable-kernel-rules.rst.
> I see that's sometimes not followed, but I think we should stick to that
> unless there's a strong reason not to.
>

Indeed, but I have adopted the

[ Upstream commit xxx ]

style in the meantime in [0] (and [1])

> If you had to make any substantial changes, I'd recommend a note above
> your S-o-B, e.g
>
> [v4.9: Renamed foo() to bar() to match xxyyzz()]
>

Sure.

> ... and regardless I usually add a [vX.Y backport] trailing my S-o-B to
> make it clear from the log where that happened.
>
> For this patch specifically, I believe that you also need to backport
> commit:
>
>   f54dada8274643e3 ("arm64: fix SSBS sanitization")
>
> ... which fixes the SSBS bit being cleared across sigreturns.
>

Coming up in 05/16

> Otherwise, this patch looks good to me.
>

Thanks.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=ssbs-v4.19-stable
[1] https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=ssbs-v4.14-stable

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