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From: Dave Martin <Dave.Martin@arm.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Mark Rutland <Mark.Rutland@arm.com>,
	Suzuki Poulose <Suzuki.Poulose@arm.com>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"will@kernel.org" <will@kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/3] arm64: cpufeature: Fix the type of no FP/SIMD capability
Date: Tue, 15 Oct 2019 15:05:42 +0100	[thread overview]
Message-ID: <20191015140541.GW27757@arm.com> (raw)
In-Reply-To: <CAKv+Gu_=jw94Hj5Vo=5w+hb5RcPR4SQvxOM02WQr9hDhyzE67g@mail.gmail.com>

On Tue, Oct 15, 2019 at 12:30:15PM +0200, Ard Biesheuvel wrote:
> On Tue, 15 Oct 2019 at 12:25, Dave Martin <Dave.Martin@arm.com> wrote:
> >
> > On Mon, Oct 14, 2019 at 06:57:30PM +0200, Ard Biesheuvel wrote:

[...]

> > > All in-kernel NEON code checks whether the NEON is usable, so I'd
> > > expect that check to return 'false' if it is too early in the boot for
> > > the NEON to be used at all.
> >
> > My concern is that the check may be done once, at probe time, for crypto
> > drivers.  If probing happens before system_supports_fpsimd() has
> > stabilised, we may be stuck with the wrong probe decision.
> >
> > So: are crypto drivers and kernel_mode_neon() users definitely only
> > probed _after_ all early CPUs are up?
> >
> 
> Isn't SMP already up when initcalls are processed?

That was my original assumption when developing SVE.  I think I
convinced myself that it was valid, but it sounds worth reinvestigating.

Assuming the assumption _is_ valid, then dropping a suitable WARN() into
system_supports_fpsimd() or cpu_has_neon() or similar may be a good idea.

Cheers
---Dave

WARNING: multiple messages have this Message-ID (diff)
From: Dave Martin <Dave.Martin@arm.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Mark Rutland <Mark.Rutland@arm.com>,
	Suzuki Poulose <Suzuki.Poulose@arm.com>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"will@kernel.org" <will@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/3] arm64: cpufeature: Fix the type of no FP/SIMD capability
Date: Tue, 15 Oct 2019 15:05:42 +0100	[thread overview]
Message-ID: <20191015140541.GW27757@arm.com> (raw)
In-Reply-To: <CAKv+Gu_=jw94Hj5Vo=5w+hb5RcPR4SQvxOM02WQr9hDhyzE67g@mail.gmail.com>

On Tue, Oct 15, 2019 at 12:30:15PM +0200, Ard Biesheuvel wrote:
> On Tue, 15 Oct 2019 at 12:25, Dave Martin <Dave.Martin@arm.com> wrote:
> >
> > On Mon, Oct 14, 2019 at 06:57:30PM +0200, Ard Biesheuvel wrote:

[...]

> > > All in-kernel NEON code checks whether the NEON is usable, so I'd
> > > expect that check to return 'false' if it is too early in the boot for
> > > the NEON to be used at all.
> >
> > My concern is that the check may be done once, at probe time, for crypto
> > drivers.  If probing happens before system_supports_fpsimd() has
> > stabilised, we may be stuck with the wrong probe decision.
> >
> > So: are crypto drivers and kernel_mode_neon() users definitely only
> > probed _after_ all early CPUs are up?
> >
> 
> Isn't SMP already up when initcalls are processed?

That was my original assumption when developing SVE.  I think I
convinced myself that it was valid, but it sounds worth reinvestigating.

Assuming the assumption _is_ valid, then dropping a suitable WARN() into
system_supports_fpsimd() or cpu_has_neon() or similar may be a good idea.

Cheers
---Dave

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2019-10-15 14:05 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10 17:15 [PATCH 0/3] arm64: Fix support for systems without FP/SIMD Suzuki K Poulose
2019-10-10 17:15 ` Suzuki K Poulose
2019-10-10 17:15 ` [PATCH 1/3] arm64: cpufeature: Fix the type of no FP/SIMD capability Suzuki K Poulose
2019-10-10 17:15   ` Suzuki K Poulose
2019-10-11 11:36   ` Dave Martin
2019-10-11 11:36     ` Dave Martin
2019-10-11 12:13     ` Suzuki K Poulose
2019-10-11 12:13       ` Suzuki K Poulose
2019-10-11 14:21       ` Dave Martin
2019-10-11 14:21         ` Dave Martin
2019-10-11 17:28         ` Suzuki K Poulose
2019-10-11 17:28           ` Suzuki K Poulose
2019-10-14 14:52           ` Dave Martin
2019-10-14 14:52             ` Dave Martin
2019-10-14 15:45             ` Suzuki K Poulose
2019-10-14 15:45               ` Suzuki K Poulose
2019-10-14 15:50               ` Dave P Martin
2019-10-14 15:50                 ` Dave P Martin
2019-10-14 16:57                 ` Ard Biesheuvel
2019-10-14 16:57                   ` Ard Biesheuvel
2019-10-15  9:44                   ` Suzuki K Poulose
2019-10-15  9:44                     ` Suzuki K Poulose
2019-10-15  9:52                     ` Ard Biesheuvel
2019-10-15  9:52                       ` Ard Biesheuvel
2019-10-15 10:24                   ` Dave Martin
2019-10-15 10:24                     ` Dave Martin
2019-10-15 10:30                     ` Ard Biesheuvel
2019-10-15 10:30                       ` Ard Biesheuvel
2019-10-15 13:03                       ` Suzuki K Poulose
2019-10-15 13:03                         ` Suzuki K Poulose
2019-10-15 13:11                         ` Ard Biesheuvel
2019-10-15 13:11                           ` Ard Biesheuvel
2019-10-15 14:05                       ` Dave Martin [this message]
2019-10-15 14:05                         ` Dave Martin
2019-10-10 17:15 ` [PATCH 2/3] arm64: nofpsmid: Clear TIF_FOREIGN_FPSTATE flag for early tasks Suzuki K Poulose
2019-10-10 17:15   ` Suzuki K Poulose
2019-10-11 11:26   ` Dave Martin
2019-10-11 11:26     ` Dave Martin
2019-10-17 12:42     ` Suzuki K Poulose
2019-10-17 12:42       ` Suzuki K Poulose
2019-10-17 16:09       ` Dave Martin
2019-10-17 16:09         ` Dave Martin
2019-10-10 17:15 ` [PATCH 3/3] arm64: cpufeature: Set the FP/SIMD compat HWCAP bits properly Suzuki K Poulose
2019-10-10 17:15   ` Suzuki K Poulose
2019-10-17  0:06 ` [PATCH 0/3] arm64: Fix support for systems without FP/SIMD Will Deacon
2019-10-17  0:06   ` Will Deacon

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