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mm, dax: introduce pfn_t_special()

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In support of removing the VM_MIXEDMAP indication from DAX VMAs,
introduce pfn_t_special() for drivers to indicate that _PAGE_SPECIAL
should be used for DAX ptes. This also helps identify drivers like
dccssblk that only want to use DAX in a read-only fashion without
get_user_pages() support.

Ideally we could delete axonram and dcssblk DAX support, but if we need
to keep it better make it explicit that axonram and dcssblk only support
a sub-set of DAX due to missing _PAGE_DEVMAP support.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2017-10-23 07:20:00 -07:00
parent 77dd66a3c6
commit 785a3fab4a
4 changed files with 31 additions and 3 deletions
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13
include/linux/pfn_t.h
View file

@ -15,8 +15,10 @@
#define PFN_SG_LAST (1ULL << (BITS_PER_LONG_LONG - 2))
#define PFN_DEV (1ULL << (BITS_PER_LONG_LONG - 3))
#define PFN_MAP (1ULL << (BITS_PER_LONG_LONG - 4))
#define PFN_SPECIAL (1ULL << (BITS_PER_LONG_LONG - 5))
#define PFN_FLAGS_TRACE \
{ PFN_SPECIAL, "SPECIAL" }, \
{ PFN_SG_CHAIN, "SG_CHAIN" }, \
{ PFN_SG_LAST, "SG_LAST" }, \
{ PFN_DEV, "DEV" }, \
@ -120,4 +122,15 @@ pud_t pud_mkdevmap(pud_t pud);
#endif
#endif /* __HAVE_ARCH_PTE_DEVMAP */
#ifdef __HAVE_ARCH_PTE_SPECIAL
static inline bool pfn_t_special(pfn_t pfn)
{
return (pfn.val & PFN_SPECIAL) == PFN_SPECIAL;
}
#else
static inline bool pfn_t_special(pfn_t pfn)
{
return false;
}
#endif /* __HAVE_ARCH_PTE_SPECIAL */
#endif /* _LINUX_PFN_T_H_ */