ARM: LPAE: don't reject mapping /dev/mem above 4GB

PATCH Superseded Sergey Dyasly 2 participants 3 messages Jul 2, 2013 – Jul 3, 2013 Arm (32-bit)

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Sergey Dyasly

author

2013-07-02 15:58 UTC #0 lore raw

PATCH v2 1/1 ARM: LPAE: don't reject mapping /dev/mem above 4GB

With LPAE enabled, physical address space is larger than 4GB. Allow mapping any part of it via /dev/mem by utilizing the same check as in arm64.

PHYS_MASK covers 40 bits with LPAE enabled and 32 bits otherwise.

Signed-off-by Sergey Dyasly <[email protected]>

---

v2:
- Removed #ifdef and changed original function as suggested by Catalin Marinas

 arch/arm/mm/mmap.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

arch/arm/mm/mmap.c +2 -4

index 10062ce..09bab92 100644
@@ -204,13 +204,11 @@ int valid_phys_addr_range(phys_addr_t addr, size_t size)
 }
 
 /*
- * We don't use supersection mappings for mmap() on /dev/mem, which
- * means that we can't map the memory area above the 4G barrier into
- * userspace.
+ * Do not allow /dev/mem mappings beyond the supported physical range.
  */
 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 {
-	return !(pfn + (size >> PAGE_SHIFT) > 0x00100000);
+	return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 }
 
 #ifdef CONFIG_STRICT_DEVMEM

Signature · 1 line

1.8.1.2

Catalin Marinas

2013-07-02 17:15 UTC #1 lore raw

PATCH v2 1/1 ARM: LPAE: don't reject mapping /dev/mem above 4GB

Quoted 21 lines · Sergey Dyasly

With LPAE enabled, physical address space is larger than 4GB. Allow mapping any part of it via /dev/mem by utilizing the same check as in arm64.
PHYS_MASK covers 40 bits with LPAE enabled and 32 bits otherwise.
Signed-off-by Sergey Dyasly <[email protected]>
---
v2:
- Removed #ifdef and changed original function as suggested by Catalin Marinas
 arch/arm/mm/mmap.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)
arch/arm/mm/mmap.c +0 -0
index 10062ce..09bab92 100644
@@ -204,13 +204,11 @@ int valid_phys_addr_range(phys_addr_t addr, size_t size)
 }
 

arch/arm/mm/mmap.c int valid_phys_addr_range(phys_addr_t addr, size_t size) · line 211

Quoted 10 lines

arch/arm/mm/mmap.c +2 -4

 /*
- * We don't use supersection mappings for mmap() on /dev/mem, which
- * means that we can't map the memory area above the 4G barrier into
- * userspace.
+ * Do not allow /dev/mem mappings beyond the supported physical range.
  */
 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 {
-	return !(pfn + (size >> PAGE_SHIFT) > 0x00100000);
+	return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);

I don't think that's what I suggested. For classic MMU ~PHYS_MASK is 0.

Signature · 1 line

Catalin

Sergey Dyasly

author

2013-07-03 15:37 UTC #2 lore raw

PATCH v2 1/1 ARM: LPAE: don't reject mapping /dev/mem above 4GB

Quoted 7 lines · On Tue, 2 Jul 2013 18:15:31 +0100 Catalin Marinas <[email protected]>…

arch/arm/mm/mmap.c int valid_phys_addr_range(phys_addr_t addr, size_t size) · line 211
Quoted 4 lines
int valid_mmap_phys_addr_range(unsigned long pfn, size_t size) {
arch/arm/mm/mmap.c +1 -1
-	return !(pfn + (size >> PAGE_SHIFT) > 0x00100000);
+	return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
I don't think that's what I suggested. For classic MMU ~PHYS_MASK is 0.

Thanks for your comments!

Indeed, I did some testing today and v2 check doesn't work at all because of 32-bit overflow in case of using '<<' operator. Also, it turned out that v1 doesn't reject mappings > 40 bit in case of LPAE (the same overflow).

I didn't want to additionally define PHYS_MASK_SHIFT, so I came up with something like:

	return (pfn + (size >> PAGE_SHIFT)) <= (1 + (PHYS_MASK >> PAGE_SHIFT))

I will post v3 tomorrow.

Best regards,
Sergey Dyasly