Re: [RFC PATCH v5 4/8] mm: tlb: Pass struct mmu_gather to flush_pmd_tlb_range

Zhenyu Ye
2020-04-01T08:51:38Z

Hi Peter,

On 2020/3/31 23:13, Peter Zijlstra wrote:
> On Tue, Mar 31, 2020 at 10:29:23PM +0800, Zhenyu Ye wrote:
>> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
>> index e2e2bef07dd2..32d4661e5a56 100644
>> --- a/include/asm-generic/pgtable.h
>> +++ b/include/asm-generic/pgtable.h
>> @@ -1160,10 +1160,10 @@ static inline int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
>> * invalidate the entire TLB which is not desitable.
>> * e.g. see arch/arc: flush_pmd_tlb_range
>> */
>> -#define flush_pmd_tlb_range(vma, addr, end) flush_tlb_range(vma, addr, end)
>> +#define flush_pmd_tlb_range(tlb, vma, addr, end) flush_tlb_range(vma, addr, end)
>> #define flush_pud_tlb_range(vma, addr, end) flush_tlb_range(vma, addr, end)
>> #else
>> -#define flush_pmd_tlb_range(vma, addr, end) BUILD_BUG()
>> +#define flush_pmd_tlb_range(tlb, vma, addr, end) BUILD_BUG()
>> #define flush_pud_tlb_range(vma, addr, end) BUILD_BUG()
>> #endif
>> #endif
>> diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
>> index 3d7c01e76efc..96c9cf77bfb5 100644
>> --- a/mm/pgtable-generic.c
>> +++ b/mm/pgtable-generic.c
>> @@ -109,8 +109,14 @@ int pmdp_set_access_flags(struct vm_area_struct *vma,
>> int changed = !pmd_same(*pmdp, entry);
>> VM_BUG_ON(address & ~HPAGE_PMD_MASK);
>> if (changed) {
>> + struct mmu_gather tlb;
>> + unsigned long tlb_start = address;
>> + unsigned long tlb_end = address + HPAGE_PMD_SIZE;
>> set_pmd_at(vma->vm_mm, address, pmdp, entry);
>> - flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
>> + tlb_gather_mmu(&tlb, vma->vm_mm, tlb_start, tlb_end);
>> + tlb.cleared_pmds = 1;
>> + flush_pmd_tlb_range(&tlb, vma, tlb_start, tlb_end);
>> + tlb_finish_mmu(&tlb, tlb_start, tlb_end);
>> }
>> return changed;
>> }
>
> This is madness. Please, carefully consider what you just wrote and what
> it will do in the generic case.
>
> Instead of trying to retro-fit flush_*tlb_range() to take an mmu_gather
> parameter, please replace them out-right.
>

I'm sorry that I'm not sure what "replace them out-right" means. Do you
mean that I should define flush_*_tlb_range like this?

#define flush_pmd_tlb_range(vma, addr, end) \
do { \
struct mmu_gather tlb; \
tlb_gather_mmu(&tlb, (vma)->vm_mm, addr, end); \
tlba.cleared_pmds = 1; \
flush_tlb_range(&tlb, vma, addr, end); \
tlb_finish_mmu(&tlb, addr, end); \
} while (0)

Thanks,
Zhenyu