linux-kernel - [PATCH 0/2] x86: allow read/write /dev/mem to access non-system RAM above high

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Message-Id: <1408548326-18665-1-git-send-email-fhrbata@redhat.com>
Date:	Wed, 20 Aug 2014 17:25:24 +0200
From:	Frantisek Hrbata <fhrbata@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-mm@...ck.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, oleg@...hat.com,
	kamaleshb@...ibm.com, hechjie@...ibm.com,
	akpm@...ux-foundation.org, dave.hansen@...el.com,
	dvlasenk@...hat.com, prarit@...hat.com, lwoodman@...hat.com,
	hannsj_uhl@...ibm.com
Subject: [PATCH 0/2] x86: allow read/write /dev/mem to access non-system RAM above high_memory

Hi,

this patch set depends on the following patches posted earlier.

[PATCH V2 1/2] x86: add arch_pfn_possible helper
   lkml: Message-Id: <1408103043-31015-2-git-send-email-fhrbata@...hat.com>
[PATCH V2 2/2] x86: add phys addr validity check for /dev/mem mmap
   lkml: Message-Id: <1408103043-31015-3-git-send-email-fhrbata@...hat.com>

This is an attempt to remove the high_memory limit for the read/write access to
/dev/mem. IMHO there is no reason for this limit on x86. It is presented in 
the generic valid_phys_addr_range, which is used only by (read|write)_mem. IIUIC
it's main purpose is for the generic xlate_dev_mem_ptr, which is using only the
direct kernel mapping __va translation. Since the valid_phys_addr_range is
called as the first check in (read|write)_mem, it basically does not allow to
access anything above high_memory on x86.

The first patch adds high_memory check to x86's (xlate|unxlate)_dev_mem_ptr, so
the direct kernel mapping can be safely used for system RAM bellow high_memory.
This is IMHO the only valid reason to use high_memory check in (read|write)_mem.

The second patch removes the high_memory check from valid_phys_addr_range,
allowing read/write to access non-system RAM above high_memory. So far this was
possible only by using mmap.

I hope I haven't overlooked something.

Many thanks

Frantisek Hrbata (2):
  x86: add high_memory check to (xlate|unxlate)_dev_mem_ptr
  x86: remove high_memory check from valid_phys_addr_range

 arch/x86/mm/ioremap.c | 9 ++++++---
 arch/x86/mm/mmap.c    | 2 +-
 2 files changed, 7 insertions(+), 4 deletions(-)

-- 
1.9.3

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