Commit 59911ca4 authored by Steve Capper's avatar Steve Capper
Browse files

ARM64: mm: Move PTE_PROT_NONE bit. 



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 or swap): Bits #0 and #1 are clear.
     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.

To resolve this ambiguity this patch moves PTE_PROT_NONE from
bit #1 to bit #2 and moves PTE_FILE from bit #2 to bit #3. The
number of swap/file bits is reduced by 1 as a consequence, leaving
60 bits for file and swap entries.

Signed-off-by: default avatarSteve Capper <steve.capper@linaro.org>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 072b1b62

arch/arm64/include/asm/pgtable.h

+12 −12
Original line number Diff line number Diff line
@@ -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_PROT_NONE		(_AT(pteval_t, 1) << 2)	/* only when !PTE_VALID */

#define PTE_FILE		(_AT(pteval_t, 1) << 3)	/* only when !pte_present() */

#define PTE_DIRTY		(_AT(pteval_t, 1) << 55)

#define PTE_SPECIAL		(_AT(pteval_t, 1) << 56)
@@ -281,12 +281,12 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; 


/*

 * Encode and decode a swap entry:

 *	bits 0-1:	present (must be zero)

 *	bit  2:		PTE_FILE

 *	bits 3-8:	swap type

 *	bits 0, 2:	present (must both be zero)

 *	bit  3:		PTE_FILE

 *	bits 4-8:	swap type

 *	bits 9-63:	swap offset

 */

#define __SWP_TYPE_SHIFT	3

#define __SWP_TYPE_SHIFT	4

#define __SWP_TYPE_BITS		6

#define __SWP_TYPE_MASK		((1 << __SWP_TYPE_BITS) - 1)

#define __SWP_OFFSET_SHIFT	(__SWP_TYPE_BITS + __SWP_TYPE_SHIFT)
@@ -306,15 +306,15 @@ 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 3-63:	file offset / PAGE_SIZE

 *	bits 0, 2:	present (must both be zero)

 *	bit  3:		PTE_FILE

 *	bits 4-63:	file offset / PAGE_SIZE

 */

#define pte_file(pte)		(pte_val(pte) & PTE_FILE)

#define pte_to_pgoff(x)		(pte_val(x) >> 3)

#define pgoff_to_pte(x)		__pte(((x) << 3) | PTE_FILE)

#define pte_to_pgoff(x)		(pte_val(x) >> 4)

#define pgoff_to_pte(x)		__pte(((x) << 4) | PTE_FILE)



#define PTE_FILE_MAX_BITS	61

#define PTE_FILE_MAX_BITS	60



extern int kern_addr_valid(unsigned long addr);

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