| Message ID | 20190913163239.125108-2-justin.he@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fix double page fault on arm64 | expand |
On Sat, Sep 14, 2019 at 12:32:38AM +0800, Jia He wrote: > On arm64 without hardware Access Flag, copying fromuser will fail because > the pte is old and cannot be marked young. So we always end up with zeroed > page after fork() + CoW for pfn mappings. we don't always have a > hardware-managed access flag on arm64. > > Hence implement arch_faults_on_old_pte on arm64 to indicate that it might > cause page fault when accessing old pte. > > Signed-off-by: Jia He <justin.he@arm.com> > --- > arch/arm64/include/asm/pgtable.h | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index e09760ece844..b41399d758df 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -868,6 +868,18 @@ static inline void update_mmu_cache(struct vm_area_struct *vma, > #define phys_to_ttbr(addr) (addr) > #endif > > +/* > + * On arm64 without hardware Access Flag, copying fromuser will fail because > + * the pte is old and cannot be marked young. So we always end up with zeroed > + * page after fork() + CoW for pfn mappings. we don't always have a > + * hardware-managed access flag on arm64. > + */ > +static inline bool arch_faults_on_old_pte(void) > +{ > + return true; Shouldn't youc check if this particular machine supports hardware access bit? > +} > +#define arch_faults_on_old_pte arch_faults_on_old_pte > + > #endif /* !__ASSEMBLY__ */ > > #endif /* __ASM_PGTABLE_H */ > -- > 2.17.1 > >
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index e09760ece844..b41399d758df 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -868,6 +868,18 @@ static inline void update_mmu_cache(struct vm_area_struct *vma, #define phys_to_ttbr(addr) (addr) #endif +/* + * On arm64 without hardware Access Flag, copying fromuser will fail because + * the pte is old and cannot be marked young. So we always end up with zeroed + * page after fork() + CoW for pfn mappings. we don't always have a + * hardware-managed access flag on arm64. + */ +static inline bool arch_faults_on_old_pte(void) +{ + return true; +} +#define arch_faults_on_old_pte arch_faults_on_old_pte + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_PGTABLE_H */
On arm64 without hardware Access Flag, copying fromuser will fail because the pte is old and cannot be marked young. So we always end up with zeroed page after fork() + CoW for pfn mappings. we don't always have a hardware-managed access flag on arm64. Hence implement arch_faults_on_old_pte on arm64 to indicate that it might cause page fault when accessing old pte. Signed-off-by: Jia He <justin.he@arm.com> --- arch/arm64/include/asm/pgtable.h | 12 ++++++++++++ 1 file changed, 12 insertions(+)