[GIT PULL] ARM: convert VFP exception handling to C code

[Ard Biesheuvel]

On Mon, 22 May 2023 at 10:03, Ard Biesheuvel <ardb at kernel.org> wrote:
>
> Hello Russell,
>
> This pull request covers the outstanding changes related to VFP exception
> handling that I implemented on top of the VFP-in-softirq policy change and
> subsequent fixes. The code changes are identical to the v2 series [0].
>
> With these changes applied, only FPE related undef exceptions are dispatched in
> the old way. Everything else is handled using undef hooks, with all logic
> implemented in C.
>
> I have tested this on a variety of platforms, including Cortex-A8 (using kernel
> mode NEON) and the original Raspberry Pi (which relies on VFP bouncing), as
> well as a host of platforms used in KernelCI [1]. All encountered issues have
> been fixed. One notable configuration that I have not been able to test is FPE,
> as it implies a OABI user space, which I don't have access to.
>
> Please pull.
>

Ping?

>
> The following changes since commit f1fcbaa18b28dec10281551dfe6ed3a3ed80e3d6:
>
>   Linux 6.4-rc2 (2023-05-14 12:51:40 -0700)
>
> are available in the Git repository at:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git tags/arm-vfp-refactor-for-rmk
>
> for you to fetch changes up to 47ba5f39eab3c2a9a1ba878159a6050f2bbfc0e2:
>
>   ARM: entry: Make asm coproc dispatch code NWFPE only (2023-05-17 15:08:22 +0200)
>
>
> [0] https://lore.kernel.org/all/20230517212808.3895190-1-ardb@kernel.org/
> [1] https://linux.kernelci.org/test/job/ardb/branch/for-kernelci/kernel/arm-vfp-refactor-for-rmk/
>
> Cc: Linus Walleij <linus.walleij at linaro.org>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
>
> ----------------------------------------------------------------
> Refactor VFP support code and reimplement in C
>
> The VFP related changes to permit kernel mode NEON in softirq context
> resulted in some issues regarding en/disabling of sofirqs from asm code,
> and this made it clear that it would be better to handle more of it from
> C code.
>
> Given that we already have infrastructure that associates undefined
> instruction exceptions with handler code based on value/mask pairs, we
> can easily move the dispatch of VFP and NEON instructions to C code once
> we reimplement the actual VFP support routine (which reasons about how
> to deal with the exception and whether any emulation is needed) in C
> code first.
>
> With those out of the way, we can drop the partial decoding logic in asm
> that reasons about which ISA is being used by user space, as the
> remaining cases are all 32-bit ARM only. This leaves a FPE specific
> routine with some iWMMXT logic that is easily duplicated in C as well,
> allowing us to move the FPE asm code into the FPE asm source file, and
> out of the shared entry code.
>
> ----------------------------------------------------------------
> Ard Biesheuvel (8):
>       ARM: vfp: Record VFP bounces as perf emulation faults
>       ARM: vfp: Remove workaround for Feroceon CPUs
>       ARM: vfp: Reimplement VFP exception entry in C code
>       ARM: kernel: Get rid of thread_info::used_cp[] array
>       ARM: vfp: Use undef hook for handling VFP exceptions
>       ARM: entry: Disregard Thumb undef exception in coproc dispatch
>       ARM: iwmmxt: Use undef hook to enable coprocessor for task
>       ARM: entry: Make asm coproc dispatch code NWFPE only
>
>  arch/arm/include/asm/thread_info.h |  17 ++-
>  arch/arm/kernel/asm-offsets.c      |   1 -
>  arch/arm/kernel/entry-armv.S       | 254 ++-----------------------------------
>  arch/arm/kernel/iwmmxt.S           |  18 ++-
>  arch/arm/kernel/pj4-cp0.c          |   1 +
>  arch/arm/kernel/process.c          |   1 -
>  arch/arm/kernel/ptrace.c           |   2 -
>  arch/arm/kernel/xscale-cp0.c       |   1 +
>  arch/arm/mm/proc-feroceon.S        |   4 +
>  arch/arm/nwfpe/entry.S             |  77 +++++++++++
>  arch/arm/vfp/Makefile              |   2 +-
>  arch/arm/vfp/entry.S               |  31 -----
>  arch/arm/vfp/vfp.h                 |   1 +
>  arch/arm/vfp/vfphw.S               | 208 ++----------------------------
>  arch/arm/vfp/vfpmodule.c           | 208 +++++++++++++++++++++---------
>  15 files changed, 286 insertions(+), 540 deletions(-)
>  delete mode 100644 arch/arm/vfp/entry.S