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From:   Geert Uytterhoeven <geert@linux-m68k.org>
To:     linux-m68k@lists.linux-m68k.org
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Geert Uytterhoeven <geert@linux-m68k.org>
Subject: [PATCH] m68k: mm: Remove check for VM_IO to fix deferred I/O
Date:   Fri, 28 Jan 2022 18:30:06 +0100
Message-Id: <20220128173006.1713210-1-geert@linux-m68k.org>
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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>
---
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))
-- 
2.25.1