Re: [PATCH, RFC 02/62] mm: Add helpers to setup zero page mappings

[Mike Rapoport]

On Wed, May 08, 2019 at 05:43:22PM +0300, Kirill A. Shutemov wrote:
> When kernel setups an encrypted page mapping, encryption KeyID is

Nit: "when kernel sets up an encrypted..."

> derived from a VMA. KeyID is going to be part of vma->vm_page_prot and
> it will be propagated transparently to page table entry on mk_pte().
> 
> But there is an exception: zero page is never encrypted and its mapping
> must use KeyID-0, regardless VMA's KeyID.
> 
> Introduce helpers that create a page table entry for zero page.
> 
> The generic implementation will be overridden by architecture-specific
> code that takes care about using correct KeyID.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  fs/dax.c                      | 3 +--
>  include/asm-generic/pgtable.h | 8 ++++++++
>  mm/huge_memory.c              | 6 ++----
>  mm/memory.c                   | 3 +--
>  mm/userfaultfd.c              | 3 +--
>  5 files changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index e5e54da1715f..6d609bff53b9 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1441,8 +1441,7 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
>  		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
>  		mm_inc_nr_ptes(vma->vm_mm);
>  	}
> -	pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
> -	pmd_entry = pmd_mkhuge(pmd_entry);
> +	pmd_entry = mk_zero_pmd(zero_page, vmf->vma->vm_page_prot);
>  	set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
>  	spin_unlock(ptl);
>  	trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index fa782fba51ee..cde8b81f6f2b 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -879,8 +879,16 @@ static inline unsigned long my_zero_pfn(unsigned long addr)
>  }
>  #endif
> 
> +#ifndef mk_zero_pte
> +#define mk_zero_pte(addr, prot) pte_mkspecial(pfn_pte(my_zero_pfn(addr), prot))
> +#endif
> +
>  #ifdef CONFIG_MMU
> 
> +#ifndef mk_zero_pmd
> +#define mk_zero_pmd(zero_page, prot) pmd_mkhuge(mk_pmd(zero_page, prot))
> +#endif
> +
>  #ifndef CONFIG_TRANSPARENT_HUGEPAGE
>  static inline int pmd_trans_huge(pmd_t pmd)
>  {
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 165ea46bf149..26c3503824ba 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -675,8 +675,7 @@ static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
>  	pmd_t entry;
>  	if (!pmd_none(*pmd))
>  		return false;
> -	entry = mk_pmd(zero_page, vma->vm_page_prot);
> -	entry = pmd_mkhuge(entry);
> +	entry = mk_zero_pmd(zero_page, vma->vm_page_prot);
>  	if (pgtable)
>  		pgtable_trans_huge_deposit(mm, pmd, pgtable);
>  	set_pmd_at(mm, haddr, pmd, entry);
> @@ -2101,8 +2100,7 @@ static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
> 
>  	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
>  		pte_t *pte, entry;
> -		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
> -		entry = pte_mkspecial(entry);
> +		entry = mk_zero_pte(haddr, vma->vm_page_prot);
>  		pte = pte_offset_map(&_pmd, haddr);
>  		VM_BUG_ON(!pte_none(*pte));
>  		set_pte_at(mm, haddr, pte, entry);
> diff --git a/mm/memory.c b/mm/memory.c
> index ab650c21bccd..c5e0c87a12b7 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2927,8 +2927,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
>  	/* Use the zero-page for reads */
>  	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
>  			!mm_forbids_zeropage(vma->vm_mm)) {
> -		entry = pte_mkspecial(pfn_pte(my_zero_pfn(vmf->address),
> -						vma->vm_page_prot));
> +		entry = mk_zero_pte(vmf->address, vma->vm_page_prot);
>  		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
>  				vmf->address, &vmf->ptl);
>  		if (!pte_none(*vmf->pte))
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index d59b5a73dfb3..ac1ce3866036 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -122,8 +122,7 @@ static int mfill_zeropage_pte(struct mm_struct *dst_mm,
>  	pgoff_t offset, max_off;
>  	struct inode *inode;
> 
> -	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
> -					 dst_vma->vm_page_prot));
> +	_dst_pte = mk_zero_pte(dst_addr, dst_vma->vm_page_prot);
>  	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
>  	if (dst_vma->vm_file) {
>  		/* the shmem MAP_PRIVATE case requires checking the i_size */
> -- 
> 2.20.1
> 

-- 
Sincerely yours,
Mike.