Re: [PATCH] m68k: mm: Remove check for VM_IO to fix deferred I/O

Michael Schmitz
2022-01-31T02:22:06Z

Hi Geert,

Am 29.01.2022 um 06:30 schrieb Geert Uytterhoeven:
> When an application accesses a mapped frame buffer backed by deferred
> I/O, it receives a segmentation fault. Fix this by removing the check
> for VM_IO in do_page_fault().
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Works fine on my Falcon030 when applied to v5.16.

Tested-by: Michael Schmitz <schmitzmic@gmail.com>

> ---
> This check was never present in a fault handler on any other
> architecture than m68k.
> Some digging revealed that it was added in v2.1.106, but I couldn't find
> an email with a patch adding it. That same kernel version extended the
> use of the hwreg_present() helper to HP9000/300, so the check might have
> been needed there, perhaps only during development?
> The Atari kernel relies heavily on hwreg_present() (both the success and
> failure cases), and these still work, at least on ARAnyM.
> ---
> arch/m68k/mm/fault.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
> index 1493cf5eac1e7a39..71aa9f6315dc8028 100644
> --- a/arch/m68k/mm/fault.c
> +++ b/arch/m68k/mm/fault.c
> @@ -93,8 +93,6 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
> vma = find_vma(mm, address);
> if (!vma)
> goto map_err;
> - if (vma->vm_flags & VM_IO)
> - goto acc_err;
> if (vma->vm_start <= address)
> goto good_area;
> if (!(vma->vm_flags & VM_GROWSDOWN))
>