[PATCH] ARC: mm: PAE40: Cast pfn to pte_t in pfn_pte() macro

From: Yuriy Kolerov
Date: Sun Nov 27 2016 - 23:10:27 EST

Originally pfn_pte(pfn, prot) macro had this definition:

__pte(((pfn) << PAGE_SHIFT) | pgprot_val(prot))

The value of pfn (Page Frame Number) is shifted to the left to get the
value of pte (Page Table Entry). Usually a 4-byte value is passed to
this macro as value of pfn. However if Linux is configured with support
of PAE40 then value of pte has 8-byte type because it must contain
additional 8 bits of the physical address. Thus if value of pfn
represents a physical page frame above of 4GB boundary then
shifting of pfn to the left by PAGE_SHIFT wipes most significant
bits of the 40-bit physical address.

As a result all physical addresses above of 4GB boundary in systems
with PAE40 are mapped to virtual address incorrectly. An error may
occur when the kernel tries to unmap such bad pages:

[ECR ]: 0x00050100 => Invalid Read @ 0x41414144 by insn @ 0x801644c6
[EFA ]: 0x41414144
[BLINK ]: unmap_page_range+0x134/0x700
[ERET ]: unmap_page_range+0x17a/0x700
[STAT32]: 0x8008021e : IE K
BTA: 0x801644c6 SP: 0x901a5e84 FP: 0x5ff35de8
LPS: 0x8026462c LPE: 0x80264630 LPC: 0x00000000
r00: 0x8fcc4fc0 r01: 0x2fe68000 r02: 0x41414140
r03: 0x2c05c000 r04: 0x2fe6a000 r05: 0x0009ffff
r06: 0x901b6898 r07: 0x2fe68000 r08: 0x00000001
r09: 0x804a807c r10: 0x0000067e r11: 0xffffffff
r12: 0x80164480
Stack Trace:

So the value of pfn must be casted to pte_t before shifting to
ensure that 40-bit address will not be truncated:

__pte(((pte_t) (pfn) << PAGE_SHIFT) | pgprot_val(prot))

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@xxxxxxxxxxxx>
arch/arc/include/asm/pgtable.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
index 89eeb37..77bc51c 100644
--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -280,7 +280,8 @@ static inline void pmd_set(pmd_t *pmdp, pte_t *ptep)

#define pte_page(pte) pfn_to_page(pte_pfn(pte))
#define mk_pte(page, prot) pfn_pte(page_to_pfn(page), prot)
-#define pfn_pte(pfn, prot) __pte(((pfn) << PAGE_SHIFT) | pgprot_val(prot))
+#define pfn_pte(pfn, prot) \
+ __pte(((pte_t) (pfn) << PAGE_SHIFT) | pgprot_val(prot))

/* Don't use virt_to_pfn for macros below: could cause truncations for PAE40*/
#define pte_pfn(pte) (pte_val(pte) >> PAGE_SHIFT)