mm: thp: Set the accessed flag for old pages on access fault.

On x86 memory accesses to pages without the ACCESSED flag set result in the
ACCESSED flag being set automatically. With the ARM architecture a page access
fault is raised instead (and it will continue to be raised until the ACCESSED
flag is set for the appropriate PTE/PMD).

For normal memory pages, handle_pte_fault will call pte_mkyoung (effectively
setting the ACCESSED flag). For transparent huge pages, pmd_mkyoung will only
be called for a write fault.

This patch ensures that faults on transparent hugepages which do not result
in a CoW update the access flags for the faulting pmd.

Cc: Chris Metcalf <cmetcalf@tilera.com>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
ARM: mm: introduce L_PTE_VALID for page table entries

For long-descriptor translation table formats, the ARMv7 architecture
defines the last two bits of the second- and third-level descriptors to
be:

	x0b	- Invalid
	01b	- Block (second-level), Reserved (third-level)
	11b	- Table (second-level), Page (third-level)

This allows us to define L_PTE_PRESENT as (3 << 0) and use this value to
create ptes directly. However, when determining whether a given pte
value is present in the low-level page table accessors, we only need to
check the least significant bit of the descriptor, allowing us to write
faulting, present entries which are required for PROT_NONE mappings.

This patch introduces L_PTE_VALID, which can be used to test whether a
pte should fault, and updates the low-level page table accessors
accordingly.

Signed-off-by: Will Deacon <will.deacon@arm.com>
ARM: mm: correct pte_same behaviour for LPAE.

For 3 levels of paging the PTE_EXT_NG bit will be set for user address ptes
that are written to a page table but not for ptes created with mk_pte.

This can cause some comparison tests made by pte_same to fail spuriously and
lead to other problems.

To correct this behaviour, we mask off PTE_EXT_NG for any pte that is
present before running the comparison.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
ARM: mm: Add support for flushing HugeTLB pages.

On ARM we use the __flush_dcache_page function to flush the dcache of pages
when needed; usually when the PG_dcache_clean bit is unset and we are setting a
PTE.

A HugeTLB page is represented as a compound page consisting of an array of
pages. Thus to flush the dcache of a HugeTLB page, one must flush more than a
single page.

This patch modifies __flush_dcache_page such that all constituent pages of a
HugeTLB page are flushed.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
ARM: mm: HugeTLB support for LPAE systems.

This patch adds support for hugetlbfs based on the x86 implementation.
It allows mapping of 2MB sections (see Documentation/vm/hugetlbpage.txt
for usage). The 64K pages configuration is not supported (section size
is 512MB in this case).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[steve.capper@arm.com: symbolic constants replace numbers in places.
Split up into multiple files, to simplify future non-LPAE support].
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
ARM: mm: HugeTLB support for non-LPAE systems.

Based on Bill Carson's HugeTLB patch, with the big difference being in the way
PTEs are passed back to the memory manager. Rather than store a "Linux Huge
PTE" separately; we make one up on the fly in huge_ptep_get. Also rather than
consider 16M supersections, we focus solely on 2x1M sections.

To construct a huge PTE on the fly we need additional information (such as the
accessed flag and dirty bit) which we choose to store in the domain bits of the
short section descriptor. In order to use these domain bits for storage, we need
to make ourselves a client for all 16 domains and this is done in head.S.

Storing extra information in the domain bits also makes it a lot easier to
implement Transparent Huge Pages, and some of the code in pgtable-2level.h is
arranged to facilitate THP support in a later patch.

Non-LPAE HugeTLB pages are incompatible with the huge page migration code
(enabled when CONFIG_MEMORY_FAILURE is selected) as that code dereferences PTEs
directly, rather than calling huge_ptep_get and set_huge_pte_at.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

Conflicts:

	arch/arm/kernel/head.S
ARM: mm: Transparent huge page support for LPAE systems.

The patch adds support for THP (transparent huge pages) to LPAE systems. When
this feature is enabled, the kernel tries to map anonymous pages as 2MB
sections where possible.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[steve.capper@arm.com: symbolic constants used, value of PMD_SECT_SPLITTING
adjusted, tlbflush.h included in pgtable.h]
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
ARM: mm: Transparent huge page support for non-LPAE systems.

Much of the required code for THP has been implemented in the earlier non-LPAE
HugeTLB patch.

One more domain bits is used (to store whether or not the THP is splitting).

Some THP helper functions are defined; and we have to re-define pmd_page such
that it distinguishes between page tables and sections.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>