linux-kernel - Re: [PATCH] m68k: mm: Remove check for VM

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Message-ID: <c1034042-f8f4-b5c9-3b0a-8d1aa1efc8e7@gmail.com>
Date:   Mon, 31 Jan 2022 15:21:57 +1300
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k: mm: Remove check for VM_IO to fix deferred I/O

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@...ux-m68k.org>

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

Tested-by: Michael Schmitz <schmitzmic@...il.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))
>