linux-kernel - Re: [PATCH 1/3] mm: set page fault address for update_mmu_cache

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Date:   Tue, 30 Jun 2020 13:09:40 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Bibo Mao <maobibo@...ngson.cn>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Daniel Silsby <dansilsby@...il.com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/3] mm: set page fault address for update_mmu_cache_pmd

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@...ngson.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