diff options
author | Anshuman Khandual <anshuman.khandual@arm.com> | 2020-09-09 10:23:02 +0530 |
---|---|---|
committer | Will Deacon <will@kernel.org> | 2020-09-11 14:57:30 +0100 |
commit | b65399f6111b03df870d8daa75b8d140c0de93f4 (patch) | |
tree | a32c0725337486742ba244bbcc55f190bcba8d8c /arch/arm64/include/asm/pgtable.h | |
parent | c048ddf86cdd066db283ce838a0049d2bbefb9e5 (diff) | |
download | linux-b65399f6111b03df870d8daa75b8d140c0de93f4.tar.bz2 |
arm64/mm: Change THP helpers to comply with generic MM semantics
pmd_present() and pmd_trans_huge() are expected to behave in the following
manner during various phases of a given PMD. It is derived from a previous
detailed discussion on this topic [1] and present THP documentation [2].
pmd_present(pmd):
- Returns true if pmd refers to system RAM with a valid pmd_page(pmd)
- Returns false if pmd refers to a migration or swap entry
pmd_trans_huge(pmd):
- Returns true if pmd refers to system RAM and is a trans huge mapping
-------------------------------------------------------------------------
| PMD states | pmd_present | pmd_trans_huge |
-------------------------------------------------------------------------
| Mapped | Yes | Yes |
-------------------------------------------------------------------------
| Splitting | Yes | Yes |
-------------------------------------------------------------------------
| Migration/Swap | No | No |
-------------------------------------------------------------------------
The problem:
PMD is first invalidated with pmdp_invalidate() before it's splitting. This
invalidation clears PMD_SECT_VALID as below.
PMD Split -> pmdp_invalidate() -> pmd_mkinvalid -> Clears PMD_SECT_VALID
Once PMD_SECT_VALID gets cleared, it results in pmd_present() return false
on the PMD entry. It will need another bit apart from PMD_SECT_VALID to re-
affirm pmd_present() as true during the THP split process. To comply with
above mentioned semantics, pmd_trans_huge() should also check pmd_present()
first before testing presence of an actual transparent huge mapping.
The solution:
Ideally PMD_TYPE_SECT should have been used here instead. But it shares the
bit position with PMD_SECT_VALID which is used for THP invalidation. Hence
it will not be there for pmd_present() check after pmdp_invalidate().
A new software defined PMD_PRESENT_INVALID (bit 59) can be set on the PMD
entry during invalidation which can help pmd_present() return true and in
recognizing the fact that it still points to memory.
This bit is transient. During the split process it will be overridden by a
page table page representing normal pages in place of erstwhile huge page.
Other pmdp_invalidate() callers always write a fresh PMD value on the entry
overriding this transient PMD_PRESENT_INVALID bit, which makes it safe.
[1]: https://lkml.org/lkml/2018/10/17/231
[2]: https://www.kernel.org/doc/Documentation/vm/transhuge.txt
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Link: https://lore.kernel.org/r/1599627183-14453-2-git-send-email-anshuman.khandual@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/include/asm/pgtable.h')
-rw-r--r-- | arch/arm64/include/asm/pgtable.h | 34 |
1 files changed, 31 insertions, 3 deletions
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index d5d3fbe73953..d8258ae8fce0 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -145,6 +145,18 @@ static inline pte_t set_pte_bit(pte_t pte, pgprot_t prot) return pte; } +static inline pmd_t clear_pmd_bit(pmd_t pmd, pgprot_t prot) +{ + pmd_val(pmd) &= ~pgprot_val(prot); + return pmd; +} + +static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot) +{ + pmd_val(pmd) |= pgprot_val(prot); + return pmd; +} + static inline pte_t pte_wrprotect(pte_t pte) { pte = clear_pte_bit(pte, __pgprot(PTE_WRITE)); @@ -363,15 +375,24 @@ static inline int pmd_protnone(pmd_t pmd) } #endif +#define pmd_present_invalid(pmd) (!!(pmd_val(pmd) & PMD_PRESENT_INVALID)) + +static inline int pmd_present(pmd_t pmd) +{ + return pte_present(pmd_pte(pmd)) || pmd_present_invalid(pmd); +} + /* * THP definitions. */ #ifdef CONFIG_TRANSPARENT_HUGEPAGE -#define pmd_trans_huge(pmd) (pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT)) +static inline int pmd_trans_huge(pmd_t pmd) +{ + return pmd_val(pmd) && pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT); +} #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ -#define pmd_present(pmd) pte_present(pmd_pte(pmd)) #define pmd_dirty(pmd) pte_dirty(pmd_pte(pmd)) #define pmd_young(pmd) pte_young(pmd_pte(pmd)) #define pmd_valid(pmd) pte_valid(pmd_pte(pmd)) @@ -381,7 +402,14 @@ static inline int pmd_protnone(pmd_t pmd) #define pmd_mkclean(pmd) pte_pmd(pte_mkclean(pmd_pte(pmd))) #define pmd_mkdirty(pmd) pte_pmd(pte_mkdirty(pmd_pte(pmd))) #define pmd_mkyoung(pmd) pte_pmd(pte_mkyoung(pmd_pte(pmd))) -#define pmd_mkinvalid(pmd) (__pmd(pmd_val(pmd) & ~PMD_SECT_VALID)) + +static inline pmd_t pmd_mkinvalid(pmd_t pmd) +{ + pmd = set_pmd_bit(pmd, __pgprot(PMD_PRESENT_INVALID)); + pmd = clear_pmd_bit(pmd, __pgprot(PMD_SECT_VALID)); + + return pmd; +} #define pmd_thp_or_huge(pmd) (pmd_huge(pmd) || pmd_trans_huge(pmd)) |