Commit cca10df1 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

sh/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE 

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by using bit 6 in the PTE,
reducing the swap type in the !CONFIG_X2TLB case to 5 bits.  Generic MM
currently only uses 5 bits for the type (MAX_SWAPFILES_SHIFT), so the
stolen bit is effectively unused.

Interrestingly, the swap type in the !CONFIG_X2TLB case could currently
overlap with the _PAGE_PRESENT bit, because there is a sneaky shift by 1
in __pte_to_swp_entry() and __swp_entry_to_pte().  Bit 0-7 in the
architecture specific swap PTE would get shifted to bit 1-8 in the PTE. 
As generic MM uses 5 bits only, this didn't matter so far.

While at it, mask the type in __swp_entry().

Link: https://lkml.kernel.org/r/20230113171026.582290-21-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 51a1007d

arch/sh/include/asm/pgtable_32.h

+42 −12
Original line number Diff line number Diff line
@@ -423,40 +423,70 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd) 
#endif



/*

 * Encode and de-code a swap entry

 * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that

 * are !pte_none() && !pte_present().

 *

 * Constraints:

 *	_PAGE_PRESENT at bit 8

 *	_PAGE_PROTNONE at bit 9

 *

 * For the normal case, we encode the swap type into bits 0:7 and the

 * swap offset into bits 10:30. For the 64-bit PTE case, we keep the

 * preserved bits in the low 32-bits and use the upper 32 as the swap

 * offset (along with a 5-bit type), following the same approach as x86

 * PAE. This keeps the logic quite simple.

 * For the normal case, we encode the swap type and offset into the swap PTE

 * such that bits 8 and 9 stay zero. For the 64-bit PTE case, we use the

 * upper 32 for the swap offset and swap type, following the same approach as

 * x86 PAE. This keeps the logic quite simple.

 *

 * As is evident by the Alpha code, if we ever get a 64-bit unsigned

 * long (swp_entry_t) to match up with the 64-bit PTEs, this all becomes

 * much cleaner..

 *

 * NOTE: We should set ZEROs at the position of _PAGE_PRESENT

 *       and _PAGE_PROTNONE bits

 */



#ifdef CONFIG_X2TLB

/*

 * Format of swap PTEs:

 *

 *   6 6 6 6 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3

 *   3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2

 *   <--------------------- offset ----------------------> < type ->

 *

 *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1

 *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0

 *   <------------------- zeroes --------------------> E 0 0 0 0 0 0

 */

#define __swp_type(x)			((x).val & 0x1f)

#define __swp_offset(x)			((x).val >> 5)

#define __swp_entry(type, offset)	((swp_entry_t){ (type) | (offset) << 5})

#define __swp_entry(type, offset)	((swp_entry_t){ ((type) & 0x1f) | (offset) << 5})

#define __pte_to_swp_entry(pte)		((swp_entry_t){ (pte).pte_high })

#define __swp_entry_to_pte(x)		((pte_t){ 0, (x).val })



#else

#define __swp_type(x)			((x).val & 0xff)

/*

 * Format of swap PTEs:

 *

 *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1

 *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0

 *   <--------------- offset ----------------> 0 0 0 0 E < type -> 0

 *

 *   E is the exclusive marker that is not stored in swap entries.

 */

#define __swp_type(x)			((x).val & 0x1f)

#define __swp_offset(x)			((x).val >> 10)

#define __swp_entry(type, offset)	((swp_entry_t){(type) | (offset) <<10})

#define __swp_entry(type, offset)	((swp_entry_t){((type) & 0x1f) | (offset) << 10})



#define __pte_to_swp_entry(pte)		((swp_entry_t) { pte_val(pte) >> 1 })

#define __swp_entry_to_pte(x)		((pte_t) { (x).val << 1 })

#endif



/* In both cases, we borrow bit 6 to store the exclusive marker in swap PTEs. */

#define _PAGE_SWP_EXCLUSIVE	_PAGE_USER



#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE

static inline int pte_swp_exclusive(pte_t pte)

{

	return pte.pte_low & _PAGE_SWP_EXCLUSIVE;

}



PTE_BIT_FUNC(low, swp_mkexclusive, |= _PAGE_SWP_EXCLUSIVE);

PTE_BIT_FUNC(low, swp_clear_exclusive, &= ~_PAGE_SWP_EXCLUSIVE);



#endif /* __ASSEMBLY__ */

#endif /* __ASM_SH_PGTABLE_32_H */