[RFC PATCH v2 08/11] ARM64: mm: Swap PTE_FILE and PTE_PROT_NONE bits.
From: Steve Capper <hidden>
Date: 2013-05-08 09:53:22
Also in:
linux-arch, linux-mm
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
Under ARM64, PTEs can be broadly categorised as follows:
- Present and valid: Bit #0 is set. The PTE is valid and memory
access to the region may fault.
- Present and invalid: Bit #0 is clear and bit #1 is set.
Represents present memory with PROT_NONE protection. The PTE
is an invalid entry, and the user fault handler will raise a
SIGSEGV.
- Not present (file): Bits #0 and #1 are clear, bit #2 is set.
Memory represented has been paged out. The PTE is an invalid
entry, and the fault handler will try and re-populate the
memory where necessary.
Huge PTEs are block descriptors that have bit #1 clear. If we wish
to represent PROT_NONE huge PTEs we then run into a problem as
there is no way to distinguish between regular and huge PTEs if we
set bit #1.
As huge PTEs are always present, the meaning of bits #1 and #2 can
be swapped for invalid PTEs. This patch swaps the PTE_FILE and
PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge
PTEs.
Signed-off-by: Steve Capper <redacted>
---
arch/arm64/include/asm/pgtable.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b1a1b59..e245260 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h@@ -25,8 +25,8 @@ * Software defined PTE bits definition. */ #define PTE_VALID (_AT(pteval_t, 1) << 0) -#define PTE_PROT_NONE (_AT(pteval_t, 1) << 1) /* only when !PTE_VALID */ -#define PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !pte_present() */ +#define PTE_FILE (_AT(pteval_t, 1) << 1) /* only when !pte_present() */ +#define PTE_PROT_NONE (_AT(pteval_t, 1) << 2) /* only when !PTE_VALID */ #define PTE_DIRTY (_AT(pteval_t, 1) << 55) #define PTE_SPECIAL (_AT(pteval_t, 1) << 56)
@@ -306,8 +306,8 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; /* * Encode and decode a file entry: - * bits 0-1: present (must be zero) - * bit 2: PTE_FILE + * bits 0 & 2: present (must be zero) + * bit 1: PTE_FILE * bits 3-63: file offset / PAGE_SIZE */ #define pte_file(pte) (pte_val(pte) & PTE_FILE)
--
1.8.1.4