Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.31 as permitted sender) client-ip=23.128.96.31;
Date:   Tue, 17 Oct 2023 15:03:24 +0100
From:   Mark Brown <broonie@kernel.org>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        open list <linux-kernel@vger.kernel.org>,
        lkft-triage@lists.linaro.org,
        linux-stable <stable@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Marc Zyngier <maz@kernel.org>
Subject: Re: selftests: ftrace: Internal error: Oops: sve_save_state
Message-ID: <39b003bc-df89-4e0b-929e-2c42354aaa86@sirena.org.uk>
References: <CA+G9fYtEGe_DhY2Ms7+L7NKsLYUomGsgqpdBj+QwDLeSg=JhGg@mail.gmail.com>
 <ad5b7442-385d-41db-9202-a36414460610@sirena.org.uk>
 <ZS6PKYMXDfAVTeLw@FVFF77S0Q05N>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="rPnpHSvbtDULm9wM"
Content-Disposition: inline
In-Reply-To: <ZS6PKYMXDfAVTeLw@FVFF77S0Q05N>
Precedence: bulk


--rPnpHSvbtDULm9wM
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Tue, Oct 17, 2023 at 02:42:01PM +0100, Mark Rutland wrote:

> So unless sve_alloc() failed, at the instant the IRQ was taken:

> * `task->thread.sve_state` should be non-NULL
> * `task->thread_info.flags & TIF_SVE` should be 0

> ... so if `task->thread.sve_state` becomes NULL, I wonder if we end up
> accidentally blatting that as part of the context switch? I can't immedaitely
> see how/

We're possibly missing a fpsimd_bind_task_to_cpu() somewhere since all
the hilarity with KVM means that we don't use the task_struct to save
state, though the task that's taking the SVE trap shouldn't be impacted
there if it didn't set TIF_SVE yet.  There *is* a window where we have
TIF_SVE set but didn't yet do the rebind but that should be in a preempt
disabled section.

--rPnpHSvbtDULm9wM
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmUulCsACgkQJNaLcl1U
h9CDrwf9F5vaNDd43zZltxM9I4iAWUwV9jTzBwFgYdJJYE7zCJi/jFFpka6sO9PS
TdCruypGFw/39o5A3Mblh6BlMiWRg+2qV/I9XcZBI8EITUFc9s/HsMF2SrcV9HWH
n41FheFZQLVmuWQHRsqUdGJOpLSSk8HZV8VUvh0MoR1KNmYzosdK1ZOR3DxPgaDr
PTar2ZaiaS3xc+EBMTfBBHExnUKKY6ASrMPHO61o82lVIFx8JGw49IGbiKAwEvpY
Bt9vnUiPQKISnKoDGpuUZC0TbTVtzoa/crdXcHJpCHTd7evZe2t6TyXOISc3kdBe
5coGUVzldurIxR14J48phXawZwmsOw==
=beHi
-----END PGP SIGNATURE-----

--rPnpHSvbtDULm9wM--