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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Michael Schmitz" <schmitzmic@gmail.com>,
        "Geert Uytterhoeven" <geert@linux-m68k.org>
Date:   Sun, 11 Nov 2018 19:49:05 +0000
Message-ID: <lsq.1541965745.448382861@decadent.org.uk>
Subject: [PATCH 3.16 082/366] m68k/mm: Adjust VM area to be unmapped by
 gap size for __iounmap()
In-Reply-To: <lsq.1541965744.387173642@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Schmitz <schmitzmic@gmail.com>

commit 3f90f9ef2dda316d64e420d5d51ba369587ccc55 upstream.

If 020/030 support is enabled, get_io_area() leaves an IO_SIZE gap
between mappings which is added to the vm_struct representing the
mapping.  __ioremap() uses the actual requested size (after alignment),
while __iounmap() is passed the size from the vm_struct.

On 020/030, early termination descriptors are used to set up mappings of
extent 'size', which are validated on unmapping. The unmapped gap of
size IO_SIZE defeats the sanity check of the pmd tables, causing
__iounmap() to loop forever on 030.

On 040/060, unmapping of page table entries does not check for a valid
mapping, so the umapping loop always completes there.

Adjust size to be unmapped by the gap that had been added in the
vm_struct prior.

This fixes the hang in atari_platform_init() reported a long time ago,
and a similar one reported by Finn recently (addressed by removing
ioremap() use from the SWIM driver.

Tested on my Falcon in 030 mode - untested but should work the same on
040/060 (the extra page tables cleared there would never have been set
up anyway).

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
[geert: Minor commit description improvements]
[geert: This was fixed in 2.4.23, but not in 2.5.x]
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 arch/m68k/mm/kmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/m68k/mm/kmap.c
+++ b/arch/m68k/mm/kmap.c
@@ -88,7 +88,8 @@ static inline void free_io_area(void *ad
 	for (p = &iolist ; (tmp = *p) ; p = &tmp->next) {
 		if (tmp->addr == addr) {
 			*p = tmp->next;
-			__iounmap(tmp->addr, tmp->size);
+			/* remove gap added in get_io_area() */
+			__iounmap(tmp->addr, tmp->size - IO_SIZE);
 			kfree(tmp);
 			return;
 		}