linux-kernel - [PATCH 1/2] x86: add high_memory check to (xlate|unxlate)_dev_mem

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Date:	Wed, 20 Aug 2014 17:25:25 +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 1/2] x86: add high_memory check to (xlate|unxlate)_dev_mem_ptr

So far (xlate|unxlate)_dev_mem_ptr for read/write /dev/mem relies on a generic
high_memory check in valid_phys_addr_range(), which does not allow to access any
memory above high_memory whatsoever. By adding the high_memory check to
(xlate|unxlate)_dev_mem_ptr, it still will be possible to use __va safely for
kernel mapped memory and it will also allow read/write to access non-system RAM
above high_memory once the high_memory check is removed from
valid_phys_addr_range.

Signed-off-by: Frantisek Hrbata <fhrbata@...hat.com>
---
 arch/x86/mm/ioremap.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index baff1da..1ae7323 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -320,8 +320,11 @@ void *xlate_dev_mem_ptr(unsigned long phys)
 	void *addr;
 	unsigned long start = phys & PAGE_MASK;
 
-	/* If page is RAM, we can use __va. Otherwise ioremap and unmap. */
-	if (page_is_ram(start >> PAGE_SHIFT))
+	/*
+	 * If page is RAM and is mapped by kernel, we can use __va.
+	 * Otherwise ioremap and unmap.
+	 */
+	if (page_is_ram(start >> PAGE_SHIFT) && phys <= __pa(high_memory))
 		return __va(phys);
 
 	addr = (void __force *)ioremap_cache(start, PAGE_SIZE);
@@ -333,7 +336,7 @@ void *xlate_dev_mem_ptr(unsigned long phys)
 
 void unxlate_dev_mem_ptr(unsigned long phys, void *addr)
 {
-	if (page_is_ram(phys >> PAGE_SHIFT))
+	if (page_is_ram(phys >> PAGE_SHIFT) && phys <= __pa(high_memory))
 		return;
 
 	iounmap((void __iomem *)((unsigned long)addr & PAGE_MASK));
-- 
1.9.3

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