From: Dan Williams <dan.j.williams@xxxxxxxxx>
Subject: mm: fix devmem_is_allowed() for sub-page System RAM intersections
Hussam reports:
I was poking around and for no real reason, I did cat /dev/mem and
strings /dev/mem. Then I saw the following warning in dmesg. I saved it
and rebooted immediately.
memremap attempted on mixed range 0x000000000009c000 size: 0x1000
------------[ cut here ]------------
WARNING: CPU: 0 PID: 11810 at kernel/memremap.c:98 memremap+0x104/0x170
[..]
Call Trace:
xlate_dev_mem_ptr+0x25/0x40
read_mem+0x89/0x1a0
__vfs_read+0x36/0x170
The memremap() implementation checks for attempts to remap System RAM with
MEMREMAP_WB and instead redirects those mapping attempts to the linear
map. However, that only works if the physical address range being
remapped is page aligned. In low memory we have situations like the
following:
00000000-00000fff : Reserved
00001000-0009fbff : System RAM
0009fc00-0009ffff : Reserved
...where System RAM intersects Reserved ranges on a sub-page page
granularity.
Given that devmem_is_allowed() special cases any attempt to map System RAM
in the first 1MB of memory, replace page_is_ram() with the more precise
region_intersects() to trap attempts to map disallowed ranges.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=199999
Link: http://lkml.kernel.org/r/152856436164.18127.2847888121707136898.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 92281dee825f ("arch: introduce memremap()")
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reported-by: Hussam Al-Tayeb <me@xxxxxxxxxxxxx>
Tested-by: Hussam Al-Tayeb <me@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/init.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff -puN arch/x86/mm/init.c~mm-fix-devmem_is_allowed-for-sub-page-system-ram-intersections arch/x86/mm/init.c
--- a/arch/x86/mm/init.c~mm-fix-devmem_is_allowed-for-sub-page-system-ram-intersections
+++ a/arch/x86/mm/init.c
@@ -706,7 +706,9 @@ void __init init_mem_mapping(void)
*/
int devmem_is_allowed(unsigned long pagenr)
{
- if (page_is_ram(pagenr)) {
+ if (region_intersects(PFN_PHYS(pagenr), PAGE_SIZE,
+ IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE)
+ != REGION_DISJOINT) {
/*
* For disallowed memory regions in the low 1MB range,
* request that the page be shown as all zeros.
_
