Re: [PATCH 1/3] mm: set page fault address for update_mmu_cache_pmd

Kirill A. Shutemov
2020-06-30T10:09:37Z

On Wed, Jun 24, 2020 at 05:26:30PM +0800, Bibo Mao wrote:
> update_mmu_cache_pmd is used to update tlb for the pmd entry by
> software. On MIPS system, the tlb entry indexed by page fault
> address maybe exists already, only that tlb entry may be small
> page, also it may be huge page. Before updating pmd entry with
> huge page size, older tlb entry need to be invalidated.
>
> Here page fault address is passed to function update_mmu_cache_pmd,
> rather than pmd huge page start address. The page fault address
> can be used for invalidating older tlb entry.
>
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
> arch/mips/include/asm/pgtable.h | 9 +++++++++
> mm/huge_memory.c | 7 ++++---
> mm/memory.c | 2 +-
> 3 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
> index dd7a0f5..bd81661 100644
> --- a/arch/mips/include/asm/pgtable.h
> +++ b/arch/mips/include/asm/pgtable.h
> @@ -554,11 +554,20 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
> #define __HAVE_ARCH_UPDATE_MMU_TLB
> #define update_mmu_tlb update_mmu_cache
>
> +extern void local_flush_tlb_page(struct vm_area_struct *vma,
> + unsigned long page);
> static inline void update_mmu_cache_pmd(struct vm_area_struct *vma,
> unsigned long address, pmd_t *pmdp)
> {
> pte_t pte = *(pte_t *)pmdp;
>
> + /*
> + * If pmd_none is true, older tlb entry will be normal page.
> + * here to invalidate older tlb entry indexed by address
> + * parameter address must be page fault address rather than
> + * start address of pmd huge page
> + */
> + local_flush_tlb_page(vma, address);

Can't say I follow what is going on.

Why local? What happens on SMP?

And don't you want to flush PMD_SIZE range around the address?

> __update_tlb(vma, address, pte);
> }
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 78c84be..0f9187b 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -780,6 +780,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> pgtable_t pgtable)
> {
> struct mm_struct *mm = vma->vm_mm;
> + unsigned long start = addr & PMD_MASK;
> pmd_t entry;
> spinlock_t *ptl;
>
> @@ -792,7 +793,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> }
> entry = pmd_mkyoung(*pmd);
> entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> - if (pmdp_set_access_flags(vma, addr, pmd, entry, 1))
> + if (pmdp_set_access_flags(vma, start, pmd, entry, 1))
> update_mmu_cache_pmd(vma, addr, pmd);
> }
>
> @@ -813,7 +814,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> pgtable = NULL;
> }
>
> - set_pmd_at(mm, addr, pmd, entry);
> + set_pmd_at(mm, start, pmd, entry);
> update_mmu_cache_pmd(vma, addr, pmd);
>
> out_unlock:
> @@ -864,7 +865,7 @@ vm_fault_t vmf_insert_pfn_pmd_prot(struct vm_fault *vmf, pfn_t pfn,
>
> track_pfn_insert(vma, &pgprot, pfn);
>
> - insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable);
> + insert_pfn_pmd(vma, vmf->address, vmf->pmd, pfn, pgprot, write, pgtable);
> return VM_FAULT_NOPAGE;
> }
> EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd_prot);
> diff --git a/mm/memory.c b/mm/memory.c
> index dc7f354..c703458 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3592,7 +3592,7 @@ static vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>
> set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
>
> - update_mmu_cache_pmd(vma, haddr, vmf->pmd);
> + update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
>
> /* fault is handled */
> ret = 0;
> --
> 1.8.3.1
>
>

--
Kirill A. Shutemov