| Message ID | 1402929159-11028-2-git-send-email-steve.capper@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Jun 16, 2014 at 03:32:38PM +0100, Steve Capper wrote: > Long descriptors on ARM are 64 bits, and some pte functions such as > pte_dirty return a bitwise-and of a flag with the pte value. If the > flag to be tested resides in the upper 32 bits of the pte, then we run > into the danger of the result being dropped if downcast. > > For example: > gather_stats(page, md, pte_dirty(*pte), 1); > where pte_dirty(*pte) is downcast to an int. > > This patch introduces a new macro pte_isset which performs the bitwise > and, then performs a double logical invert (where needed) to ensure > predictable downcasting. The logical inverse pte_isclear is also > introduced. > > Equivalent pmd functions for Transparent HugePages have also been > added. > > Signed-off-by: Steve Capper <steve.capper@linaro.org> > --- > arch/arm/include/asm/pgtable-3level.h | 10 +++++++--- > arch/arm/include/asm/pgtable.h | 18 +++++++++++------- > 2 files changed, 18 insertions(+), 10 deletions(-) > > diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h > index 85c60ad..bde49f9 100644 > --- a/arch/arm/include/asm/pgtable-3level.h > +++ b/arch/arm/include/asm/pgtable-3level.h > @@ -207,16 +207,20 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr) > #define pte_huge(pte) (pte_val(pte) && !(pte_val(pte) & PTE_TABLE_BIT)) > #define pte_mkhuge(pte) (__pte(pte_val(pte) & ~PTE_TABLE_BIT)) > > -#define pmd_young(pmd) (pmd_val(pmd) & PMD_SECT_AF) > +#define pmd_isset(pmd, val) ((u32)(val) == (val) ? pmd_val(pmd) & (val) \ > + : !!(pmd_val(pmd) & (val))) What does GCC generate for this as opposed to an unconditional !!? Will
On Fri, Jun 20, 2014 at 10:12:26AM +0100, Will Deacon wrote: > On Mon, Jun 16, 2014 at 03:32:38PM +0100, Steve Capper wrote: > > -#define pmd_young(pmd) (pmd_val(pmd) & PMD_SECT_AF) > > +#define pmd_isset(pmd, val) ((u32)(val) == (val) ? pmd_val(pmd) & (val) \ > > + : !!(pmd_val(pmd) & (val))) > > What does GCC generate for this as opposed to an unconditional !!? For any constant "val", the result of (u32)(val) == (val) is also a constant, so GCC should evaluate it at build time and not run time. An unconditional !! would result in GCC doing the test and then constructing code to turn it into a zero-or-one condition, and with complicated tests, it can really add a lot of additional complexity, even if it can properly optimise the simple case.
diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h index 85c60ad..bde49f9 100644 --- a/arch/arm/include/asm/pgtable-3level.h +++ b/arch/arm/include/asm/pgtable-3level.h @@ -207,16 +207,20 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr) #define pte_huge(pte) (pte_val(pte) && !(pte_val(pte) & PTE_TABLE_BIT)) #define pte_mkhuge(pte) (__pte(pte_val(pte) & ~PTE_TABLE_BIT)) -#define pmd_young(pmd) (pmd_val(pmd) & PMD_SECT_AF) +#define pmd_isset(pmd, val) ((u32)(val) == (val) ? pmd_val(pmd) & (val) \ + : !!(pmd_val(pmd) & (val))) +#define pmd_isclear(pmd, val) (!(pmd_val(pmd) & (val))) + +#define pmd_young(pmd) (pmd_isset((pmd), PMD_SECT_AF)) #define __HAVE_ARCH_PMD_WRITE -#define pmd_write(pmd) (!(pmd_val(pmd) & PMD_SECT_RDONLY)) +#define pmd_write(pmd) (pmd_isclear((pmd), PMD_SECT_RDONLY)) #define pmd_hugewillfault(pmd) (!pmd_young(pmd) || !pmd_write(pmd)) #define pmd_thp_or_huge(pmd) (pmd_huge(pmd) || pmd_trans_huge(pmd)) #ifdef CONFIG_TRANSPARENT_HUGEPAGE -#define pmd_trans_huge(pmd) (pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT)) +#define pmd_trans_huge(pmd) (pmd_val(pmd) && pmd_isclear((pmd), PMD_TABLE_BIT)) #define pmd_trans_splitting(pmd) (pmd_val(pmd) & PMD_SECT_SPLITTING) #endif diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h index 5478e5d..01baef0 100644 --- a/arch/arm/include/asm/pgtable.h +++ b/arch/arm/include/asm/pgtable.h @@ -214,18 +214,22 @@ static inline pte_t *pmd_page_vaddr(pmd_t pmd) #define pte_clear(mm,addr,ptep) set_pte_ext(ptep, __pte(0), 0) +#define pte_isset(pte, val) ((u32)(val) == (val) ? pte_val(pte) & (val) \ + : !!(pte_val(pte) & (val))) +#define pte_isclear(pte, val) (!(pte_val(pte) & (val))) + #define pte_none(pte) (!pte_val(pte)) -#define pte_present(pte) (pte_val(pte) & L_PTE_PRESENT) -#define pte_valid(pte) (pte_val(pte) & L_PTE_VALID) +#define pte_present(pte) (pte_isset((pte), L_PTE_PRESENT)) +#define pte_valid(pte) (pte_isset((pte), L_PTE_VALID)) #define pte_accessible(mm, pte) (mm_tlb_flush_pending(mm) ? pte_present(pte) : pte_valid(pte)) -#define pte_write(pte) (!(pte_val(pte) & L_PTE_RDONLY)) -#define pte_dirty(pte) (pte_val(pte) & L_PTE_DIRTY) -#define pte_young(pte) (pte_val(pte) & L_PTE_YOUNG) -#define pte_exec(pte) (!(pte_val(pte) & L_PTE_XN)) +#define pte_write(pte) (pte_isclear((pte), L_PTE_RDONLY)) +#define pte_dirty(pte) (pte_isset((pte), L_PTE_DIRTY)) +#define pte_young(pte) (pte_isset((pte), L_PTE_YOUNG)) +#define pte_exec(pte) (pte_isclear((pte), L_PTE_XN)) #define pte_special(pte) (0) #define pte_valid_user(pte) \ - (pte_valid(pte) && (pte_val(pte) & L_PTE_USER) && pte_young(pte)) + (pte_valid(pte) && pte_isset((pte), L_PTE_USER) && pte_young(pte)) #if __LINUX_ARM_ARCH__ < 6 static inline void __sync_icache_dcache(pte_t pteval)
Long descriptors on ARM are 64 bits, and some pte functions such as pte_dirty return a bitwise-and of a flag with the pte value. If the flag to be tested resides in the upper 32 bits of the pte, then we run into the danger of the result being dropped if downcast. For example: gather_stats(page, md, pte_dirty(*pte), 1); where pte_dirty(*pte) is downcast to an int. This patch introduces a new macro pte_isset which performs the bitwise and, then performs a double logical invert (where needed) to ensure predictable downcasting. The logical inverse pte_isclear is also introduced. Equivalent pmd functions for Transparent HugePages have also been added. Signed-off-by: Steve Capper <steve.capper@linaro.org> --- arch/arm/include/asm/pgtable-3level.h | 10 +++++++--- arch/arm/include/asm/pgtable.h | 18 +++++++++++------- 2 files changed, 18 insertions(+), 10 deletions(-)