Re: git: b4efc6277634 - main - LinuxKPI: Do not use explicit context in FPU sections on powerpc64

From: John Baldwin <jhb_at_FreeBSD.org>
Date: Wed, 27 Dec 2023 17:05:35 UTC 
On 12/24/23 5:20 AM, Vladimir Kondratyev wrote:
> The branch main has been updated by wulf:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=b4efc62776344a9aaada5a0866e453e528a0e977
> 
> commit b4efc62776344a9aaada5a0866e453e528a0e977
> Author:     Vladimir Kondratyev <wulf@FreeBSD.org>
> AuthorDate: 2023-12-24 12:48:06 +0000
> Commit:     Vladimir Kondratyev <wulf@FreeBSD.org>
> CommitDate: 2023-12-24 12:48:06 +0000
> 
>      LinuxKPI: Do not use explicit context in FPU sections on powerpc64
>      
>      It is not supported yet.
>      
>      Sponsored by:   Serenity Cyber Security, LLC
>      Fixes:  5a3bd281672b ("LinuxKPI: Add explicit software context to FPU sections")
>      MFC after:      1 week
> ---
>   sys/compat/linuxkpi/common/include/linux/compat.h | 5 -----
>   sys/compat/linuxkpi/common/src/linux_current.c    | 9 ++++++---
>   sys/compat/linuxkpi/common/src/linux_fpu.c        | 3 ++-
>   3 files changed, 8 insertions(+), 9 deletions(-)

Do you need explicit contexts at all?  That is, can you not just
use FPU_KERN_NOCTX all the time?  Most code in the tree now uses
FPU_KERN_NOCTX now (all the crypto drivers for example), and I've
been thinking about removing support for the !FPU_KERN_NOCTX case.
Is there a reason drm-kmod can't use FPU_KERN_NOCTX?  Do you really
need to save FPU registers in one block of code wrapped by fpu_kern_*
and then use those register values in a future section wrapped by
fpu_kern_*?

-- 
John Baldwin