Re: [PATCH v9 14/24] mm: Introduce __maybe_mkwrite()

[David Rientjes <rientjes@google.com>]

On Tue, 13 Mar 2018, Laurent Dufour wrote:

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index dfa81a638b7c..a84ddc218bbd 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -684,13 +684,18 @@ void free_compound_page(struct page *page);
>   * pte_mkwrite.  But get_user_pages can cause write faults for mappings
>   * that do not have writing enabled, when used by access_process_vm.
>   */
> -static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> +static inline pte_t __maybe_mkwrite(pte_t pte, unsigned long vma_flags)
>  {
> -	if (likely(vma->vm_flags & VM_WRITE))
> +	if (likely(vma_flags & VM_WRITE))
>  		pte = pte_mkwrite(pte);
>  	return pte;
>  }
>  
> +static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> +{
> +	return __maybe_mkwrite(pte, vma->vm_flags);
> +}
> +
>  int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
>  		struct page *page);
>  int finish_fault(struct vm_fault *vmf);
> diff --git a/mm/memory.c b/mm/memory.c
> index 0a0a483d9a65..af0338fbc34d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2472,7 +2472,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
>  
>  	flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
>  	entry = pte_mkyoung(vmf->orig_pte);
> -	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> +	entry = __maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
>  	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
>  		update_mmu_cache(vma, vmf->address, vmf->pte);
>  	pte_unmap_unlock(vmf->pte, vmf->ptl);
> @@ -2549,8 +2549,8 @@ static int wp_page_copy(struct vm_fault *vmf)
>  			inc_mm_counter_fast(mm, MM_ANONPAGES);
>  		}
>  		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
> -		entry = mk_pte(new_page, vma->vm_page_prot);
> -		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> +		entry = mk_pte(new_page, vmf->vma_page_prot);
> +		entry = __maybe_mkwrite(pte_mkdirty(entry), vmf->vma_flags);
>  		/*
>  		 * Clear the pte entry and flush it first, before updating the
>  		 * pte with the new entry. This will avoid a race condition

Don't you also need to do this in do_swap_page()?

diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3067,9 +3067,9 @@ int do_swap_page(struct vm_fault *vmf)
 
 	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 	dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
-	pte = mk_pte(page, vma->vm_page_prot);
+	pte = mk_pte(page, vmf->vma_page_prot);
 	if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
-		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
+		pte = __maybe_mkwrite(pte_mkdirty(pte), vmf->vma_flags);
 		vmf->flags &= ~FAULT_FLAG_WRITE;
 		ret |= VM_FAULT_WRITE;
 		exclusive = RMAP_EXCLUSIVE;