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From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Tue, 12 Dec 2023 14:54:33 +0100
Message-ID: <CAMuHMdWca4Mhuqg90b5zJhRJ+HneNjzHtXC3w24_k=t182ryfw@mail.gmail.com>
Subject: Re: [PATCH v4 1/4] arm64: fpsimd: Drop unneeded 'busy' flag
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@google.com>, 
	linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, 
	Marc Zyngier <maz@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Kees Cook <keescook@chromium.org>, 
	Catalin Marinas <catalin.marinas@arm.com>, Mark Brown <broonie@kernel.org>, 
	Eric Biggers <ebiggers@google.com>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, 
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>
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Hi Ard,

On Tue, Dec 12, 2023 at 1:59=E2=80=AFPM Ard Biesheuvel <ardb@kernel.org> wr=
ote:
> On Tue, 12 Dec 2023 at 13:34, Geert Uytterhoeven <geert@linux-m68k.org> w=
rote:
> > On Tue, Dec 12, 2023 at 1:30=E2=80=AFPM Will Deacon <will@kernel.org> w=
rote:
> > > On Tue, Dec 12, 2023 at 12:27:50PM +0100, Geert Uytterhoeven wrote:
> > > > On Fri, Dec 8, 2023 at 12:34=E2=80=AFPM Ard Biesheuvel <ardb@google=
.com> wrote:
> > > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > > > Kernel mode NEON will preserve the user mode FPSIMD state by savi=
ng it
> > > > > into the task struct before clobbering the registers. In order to=
 avoid
> > > > > the need for preserving kernel mode state too, we disallow nested=
 use of
> > > > > kernel mode NEON, i..e, use in softirq context while the interrup=
ted
> > > > > task context was using kernel mode NEON too.
> > > > >
> > > > > Originally, this policy was implemented using a per-CPU flag whic=
h was
> > > > > exposed via may_use_simd(), requiring the users of the kernel mod=
e NEON
> > > > > to deal with the possibility that it might return false, and havi=
ng NEON
> > > > > and non-NEON code paths. This policy was changed by commit
> > > > > 13150149aa6ded1 ("arm64: fpsimd: run kernel mode NEON with softir=
qs
> > > > > disabled"), and now, softirq processing is disabled entirely inst=
ead,
> > > > > and so may_use_simd() can never fail when called from task or sof=
tirq
> > > > > context.
> > > > >
> > > > > This means we can drop the fpsimd_context_busy flag entirely, and
> > > > > instead, ensure that we disable softirq processing in places wher=
e we
> > > > > formerly relied on the flag for preventing races in the FPSIMD pr=
eserve
> > > > > routines.
> > > > >
> > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > > Reviewed-by: Mark Brown <broonie@kernel.org>
> > > >
> > > > Thanks for your patch, which is now commit e109130b0e5ec3fd
> > > > ("arm64: fpsimd: Drop unneeded 'busy' flag") in arm64/for-next/core
> > > > and next-20231212.
> > > >
> > > > I have bisected the following warning during boot (on Salvator-XS w=
ith
> > > > R-Car H3 ES2.0 and on White-Hawk with R-Car V4H) followed by a lock=
-up
> > > > (on Salvator-XS) to this commit:
> > >
> > > Please can you provide the output from the warning and, if possible, =
a
> >
> > Oops, how did that log disappear?
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 0 at kernel/softirq.c:361 __local_bh_enable_ip+0x1=
a4/0x1c8
> > CPU: 0 PID: 0 Comm: swapper/0 Not tainted
> > 6.7.0-rc3-arm64-renesas-00001-ge109130b0e5e #2383
> > Hardware name: Renesas Salvator-X 2nd version board based on r8a77951 (=
DT)
> > pstate: 400000c5 (nZcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=3D--)
> > pc : __local_bh_enable_ip+0x1a4/0x1c8
> > lr : fpsimd_save_and_flush_cpu_state+0x4c/0x58
> > sp : ffff800081703bb0
> > x29: ffff800081703bb0 x28: ffff80008171c6b0 x27: ffff8000800167fc
> > x26: 0000000000000000 x25: 0000000000000000 x24: ffff800081710a68
> > x23: ffff8000813c4008 x22: ffff800081703ca4 x21: 0000000000000000
> > x20: ffff8000800167c8 x19: 0000000000000200 x18: ffffffffffffffff
> > x17: ffff0004c27f2400 x16: 0000000000000001 x15: 0000000000000003
> > x14: 0000000000000000 x13: 0000000000000003 x12: 0000000000000000
> > x11: 071c71c71c71c71c x10: ffff800082086b88 x9 : 0000000000000000
> > x8 : ffff80008203ab50 x7 : 0000000000000bb0 x6 : ffff80008203b700
> > x5 : ffff80067e2ee000 x4 : 0000000000000202 x3 : ffff80067e2ee000
> > x2 : ffff80067e2ee000 x1 : ffff800081719fc0 x0 : 0000000100000202
> > Call trace:
> >  __local_bh_enable_ip+0x1a4/0x1c8
> >  fpsimd_save_and_flush_cpu_state+0x4c/0x58
> >  fpsimd_cpu_pm_notifier+0x1c/0x28
> >  notifier_call_chain+0x9c/0x174
> >  raw_notifier_call_chain_robust+0x40/0x98
> >  cpu_pm_enter+0x3c/0x70
> >  psci_enter_idle_state+0x28/0x78
> >  cpuidle_enter_state+0xe4/0x568
> >  cpuidle_enter+0x34/0x48
> >  do_idle+0x214/0x290
>
> Thanks for the report. I missed the fact that this is called from the
> idle path. The old code just set and cleared the 'busy' flag there
>
> Could you please check whether this fixes the issue? Thanks.

Thanks, that fixed the issue!

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
.org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds