From: Linus Walleij <linus.walleij@linaro.org>
To: Ard Biesheuvel <ardb@kernel.org>,
Nicolas Pitre <nico@fluxnic.net>,
Nicolas Pitre <npitre@baylibre.com>
Cc: linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk,
Frederic Weisbecker <frederic@kernel.org>,
Guenter Roeck <linux@roeck-us.net>,
Peter Zijlstra <peterz@infradead.org>,
Arnd Bergmann <arnd@arndb.de>,
stable@vger.kernel.org
Subject: Re: [PATCH v4 04/12] ARM: entry: Fix iWMMXT TIF flag handling
Date: Tue, 21 Mar 2023 15:32:21 +0100 [thread overview]
Message-ID: <CACRpkdbRf9NL4+m+bJZ16x5uCMb2rDYmBk3xTwmVDFykDTmnMQ@mail.gmail.com> (raw)
In-Reply-To: <20230320131845.3138015-5-ardb@kernel.org>
On Mon, Mar 20, 2023 at 2:19 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> The conditional MOVS instruction that appears to have been added to test
> for the TIF_USING_IWMMXT thread_info flag only sets the N and Z
> condition flags and register R7, none of which are referenced in the
> subsequent code. This means that the instruction does nothing, which
> means that we might misidentify faulting FPE instructions as iWMMXT
> instructions on kernels that were built to support both.
>
> This seems to have been part of the original submission of the code, and
> so this has never worked as intended, and nobody ever noticed, and so we
> might decide to just leave this as-is. However, with the ongoing move
> towards multiplatform kernels, the issue becomes more likely to
> manifest, and so it is better to fix it.
>
> So check whether we are dealing with an undef exception regarding
> coprocessor index #0 or #1, and if so, load the thread_info flag and
> only dispatch it as a iWMMXT trap if the flag is set.
>
> Cc: <stable@vger.kernel.org> # v2.6.9+
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Looks right to me.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
The code dates back before git history, but it was introduced in
Linux v2.6.9 and it looks like Nicolas Pitre wrote it so let's just
ping him and see what he remembers about this!
Yours,
Linus Walleij
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next prev parent reply other threads:[~2023-03-21 14:33 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-20 13:18 [PATCH v4 00/12] ARM: vfp: Switch to C API to en/disable softirqs Ard Biesheuvel
2023-03-20 13:18 ` [PATCH v4 01/12] ARM: vfp: Pass thread_info pointer to vfp_support_entry Ard Biesheuvel
2023-03-20 13:18 ` [PATCH v4 02/12] ARM: vfp: Pass successful return address via register R3 Ard Biesheuvel
2023-03-20 13:18 ` [PATCH v4 03/12] ARM: vfp: Fix broken softirq handling with instrumentation enabled Ard Biesheuvel
2023-04-09 14:29 ` Linux regression tracking (Thorsten Leemhuis)
2023-04-10 20:15 ` Guenter Roeck
2023-03-20 13:18 ` [PATCH v4 04/12] ARM: entry: Fix iWMMXT TIF flag handling Ard Biesheuvel
2023-03-21 14:32 ` Linus Walleij [this message]
2023-03-21 19:19 ` Nicolas Pitre
2023-03-21 19:32 ` Ard Biesheuvel
2023-03-20 13:18 ` [PATCH v4 05/12] ARM: vfp: Record VFP bounces as perf emulation faults Ard Biesheuvel
2023-03-21 14:33 ` Linus Walleij
2023-03-20 13:18 ` [PATCH v4 06/12] ARM: vfp: Remove workaround for Feroceon CPUs Ard Biesheuvel
2023-03-21 14:44 ` Linus Walleij
2023-03-21 15:42 ` Ard Biesheuvel
2023-03-21 20:40 ` Linus Walleij
2023-03-22 7:26 ` Arnd Bergmann
2023-03-21 20:00 ` Nicolas Pitre
2023-03-20 13:18 ` [PATCH v4 07/12] ARM: vfp: Reimplement VFP exception entry in C code Ard Biesheuvel
2023-03-20 13:18 ` [PATCH v4 08/12] ARM: kernel: Get rid of thread_info::used_cp[] array Ard Biesheuvel
2023-03-21 14:58 ` Linus Walleij
2023-03-20 13:18 ` [PATCH v4 09/12] ARM: vfp: Use undef hook for handling VFP exceptions Ard Biesheuvel
2023-03-21 14:59 ` Linus Walleij
2023-03-21 15:41 ` Ard Biesheuvel
2023-03-20 13:18 ` [PATCH v4 10/12] ARM: entry: Disregard Thumb undef exception in coproc dispatch Ard Biesheuvel
2023-03-21 15:05 ` Linus Walleij
2023-03-20 13:18 ` [PATCH v4 11/12] ARM: iwmmxt: Use undef hook to enable coprocessor for task Ard Biesheuvel
2023-03-21 15:06 ` Linus Walleij
2023-03-20 13:18 ` [PATCH v4 12/12] ARM: entry: Make asm coproc dispatch code NWFPE only Ard Biesheuvel
2023-03-21 15:11 ` Linus Walleij
2023-03-23 2:44 ` [PATCH v4 00/12] ARM: vfp: Switch to C API to en/disable softirqs Guenter Roeck
2023-03-23 8:33 ` Ard Biesheuvel
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