Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 2 Jun 2022 10:22:52 +0200
From:   Mark Brown <broonie@kernel.org>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     kernel test robot <lkp@intel.com>, kbuild-all@lists.01.org,
        linux-kernel@vger.kernel.org
Subject: Re: arch/arm64/kernel/fpsimd.c:1944:55: sparse: sparse: dereference
 of noderef expression
Message-ID: <YphzXEcBKARluNVM@sirena.org.uk>
References: <202205280635.XKlMkfKD-lkp@intel.com>
 <YpZJBoxqvaCLRQfX@arm.com>
 <YpcaTwI4SvV3IrwF@sirena.org.uk>
 <YpeZ0M5we/0yzxVC@arm.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="PeXLahpez0u4U49V"
Content-Disposition: inline
In-Reply-To: <YpeZ0M5we/0yzxVC@arm.com>
Precedence: bulk


--PeXLahpez0u4U49V
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Wed, Jun 01, 2022 at 05:54:40PM +0100, Catalin Marinas wrote:
> On Wed, Jun 01, 2022 at 09:50:39AM +0200, Mark Brown wrote:
> > On Tue, May 31, 2022 at 05:57:42PM +0100, Catalin Marinas wrote:

> > Yes, that looks right - feel free to add my Reviewed-by or I'll
> > do that when I see the patch sent properly.

> I'm no longer convinced that's the right fix. In __efi_fpsimd_begin(),
> ffr is true if either !system_supports_fa64() or SVCR.SM is set. The FFR
> state would be saved in this case.

That's the wrong way round - we should only save FFR if we have
FA64 or SVCR.SM is *not* set.  Checking again efi_fpsimd_begin()
is wrong.

> In __efi_fpsimd_end(), shouldn't we just restore the FFR state if
> efi_sm_state, irrespective of system_supports_fa64() (as it was checked
> in the beginning). Something like:

No, we should restore it only if we saved it.  The below should
resolve things but it's completely untested:

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 819979398127..3c66a061ff6f 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1916,10 +1916,11 @@ void __efi_fpsimd_begin(void)
 			if (system_supports_sme()) {
 				svcr =3D read_sysreg_s(SYS_SVCR);
=20
-				if (!system_supports_fa64())
-					ffr =3D svcr & SVCR_SM_MASK;
+				__this_cpu_write(efi_sm_state,
+						 svcr & SVCR_SM_MASK);
=20
-				__this_cpu_write(efi_sm_state, ffr);
+				if (!system_supports_fa64())
+					ffr =3D !(svcr & SVCR_SM_MASK);
 			}
=20
 			sve_save_state(sve_state + sve_ffr_offset(sve_max_vl()),
@@ -1965,7 +1966,7 @@ void __efi_fpsimd_end(void)
 							   0,
 							   SVCR_SM_MASK);
 					if (!system_supports_fa64())
-						ffr =3D efi_sm_state;
+						ffr =3D false;
 				}
 			}
=20

--PeXLahpez0u4U49V
Content-Type: application/pgp-signature; name="signature.asc"

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

iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmKYc1wACgkQJNaLcl1U
h9C2UQf+J0ClE8Vhx0jAbXXsz7P/saaEv/Mcp7gLzO4V4ATcXH8gQox+kztlh7tJ
pGRdvskRugJ6Tg54xr9tdGKSlwFJW8nH0KLEAIev9Qgj0z1u77otapePtwRdunZZ
uvFFOjqmHMJMyZnRXbbAqe6+wma3on89TmE7PCTfjBIQqytronG2YOBUI2n4l3Rk
JJJBqWdoYbU/idvoujgon+AnFxRZDkHmzf+U5FGWW6aSu9WOddSxPCDVttyVOrj9
hYsmXu60aPEh2gzjg+WJH35nzUyAGPX4VDT3IrHBYAMcpmP4XUJj/2yQP4TpMHOd
rY9ZwRBwgbiUAD+MaQoLa6L0OfcQ5g==
=Phwp
-----END PGP SIGNATURE-----

--PeXLahpez0u4U49V--