Re: [PATCH v3 03/12] device-dax: Enable page_mapping()

[Jan Kara <jack@suse.cz>]

On Mon 04-06-18 16:11:55, Dan Williams wrote:
> In support of enabling memory_failure() handling for device-dax
> mappings, set the ->mapping association of pages backing device-dax
> mappings. The rmap implementation requires page_mapping() to return the
> address_space hosting the vmas that map the page.
> 
> The ->mapping pointer is never cleared. There is no possibility for the
> page to become associated with another address_space while the device is
> enabled. When the device is disabled the 'struct page' array for the
> device is destroyed / later reinitialized to zero.
> 
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  drivers/dax/device.c |   55 +++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 38 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 686de08e120b..7ec246549721 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -245,13 +245,12 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
>  }
>  
>  static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
> -				struct vm_fault *vmf)
> +				struct vm_fault *vmf, pfn_t *pfn)
>  {
>  	struct vm_area_struct *vma = vmf->vma;
>  	struct device *dev = &dev_dax->dev;
>  	struct dax_region *dax_region;
>  	phys_addr_t phys;
> -	pfn_t pfn;
>  	unsigned int fault_size = PAGE_SIZE;
>  
>  	if (check_vma(dev_dax, vma, __func__))
> @@ -273,13 +272,13 @@ static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
>  		return VM_FAULT_SIGBUS;
>  	}
>  
> -	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
> +	*pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
>  
> -	return vmf_insert_mixed(vma, vmf->address, pfn);
> +	return vmf_insert_mixed(vma, vmf->address, *pfn);
>  }
>  
>  static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
> -				struct vm_fault *vmf)
> +				struct vm_fault *vmf, pfn_t *pfn)
>  {
>  	unsigned long pmd_addr = vmf->address & PMD_MASK;
>  	struct vm_area_struct *vma = vmf->vma;
> @@ -287,7 +286,6 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
>  	struct dax_region *dax_region;
>  	phys_addr_t phys;
>  	pgoff_t pgoff;
> -	pfn_t pfn;
>  	unsigned int fault_size = PMD_SIZE;
>  
>  	if (check_vma(dev_dax, vma, __func__))
> @@ -322,15 +320,15 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
>  		return VM_FAULT_SIGBUS;
>  	}
>  
> -	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
> +	*pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
>  
> -	return vmf_insert_pfn_pmd(vma, vmf->address, vmf->pmd, pfn,
> +	return vmf_insert_pfn_pmd(vma, vmf->address, vmf->pmd, *pfn,
>  			vmf->flags & FAULT_FLAG_WRITE);
>  }
>  
>  #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>  static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
> -				struct vm_fault *vmf)
> +				struct vm_fault *vmf, pfn_t *pfn)
>  {
>  	unsigned long pud_addr = vmf->address & PUD_MASK;
>  	struct vm_area_struct *vma = vmf->vma;
> @@ -338,7 +336,6 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  	struct dax_region *dax_region;
>  	phys_addr_t phys;
>  	pgoff_t pgoff;
> -	pfn_t pfn;
>  	unsigned int fault_size = PUD_SIZE;
>  
>  
> @@ -374,14 +371,14 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  		return VM_FAULT_SIGBUS;
>  	}
>  
> -	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
> +	*pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
>  
> -	return vmf_insert_pfn_pud(vma, vmf->address, vmf->pud, pfn,
> +	return vmf_insert_pfn_pud(vma, vmf->address, vmf->pud, *pfn,
>  			vmf->flags & FAULT_FLAG_WRITE);
>  }
>  #else
>  static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
> -				struct vm_fault *vmf)
> +				struct vm_fault *vmf, pfn_t *pfn)
>  {
>  	return VM_FAULT_FALLBACK;
>  }
> @@ -390,9 +387,11 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
>  		enum page_entry_size pe_size)
>  {
> -	int rc, id;
>  	struct vm_area_struct *vma = vmf->vma;
>  	struct file *filp = vma->vm_file;
> +	unsigned long fault_size;
> +	int rc, id;
> +	pfn_t pfn;
>  	struct dev_dax *dev_dax = filp->private_data;
>  
>  	dev_dbg(&dev_dax->dev, "%s: %s (%#lx - %#lx) size = %d\n", current->comm,
> @@ -402,17 +401,39 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
>  	id = dax_read_lock();
>  	switch (pe_size) {
>  	case PE_SIZE_PTE:
> -		rc = __dev_dax_pte_fault(dev_dax, vmf);
> +		fault_size = PAGE_SIZE;
> +		rc = __dev_dax_pte_fault(dev_dax, vmf, &pfn);
>  		break;
>  	case PE_SIZE_PMD:
> -		rc = __dev_dax_pmd_fault(dev_dax, vmf);
> +		fault_size = PMD_SIZE;
> +		rc = __dev_dax_pmd_fault(dev_dax, vmf, &pfn);
>  		break;
>  	case PE_SIZE_PUD:
> -		rc = __dev_dax_pud_fault(dev_dax, vmf);
> +		fault_size = PUD_SIZE;
> +		rc = __dev_dax_pud_fault(dev_dax, vmf, &pfn);
>  		break;
>  	default:
>  		rc = VM_FAULT_SIGBUS;
>  	}
> +
> +	if (rc == VM_FAULT_NOPAGE) {
> +		unsigned long i;
> +
> +		/*
> +		 * In the device-dax case the only possibility for a
> +		 * VM_FAULT_NOPAGE result is when device-dax capacity is
> +		 * mapped. No need to consider the zero page, or racing
> +		 * conflicting mappings.
> +		 */
> +		for (i = 0; i < fault_size / PAGE_SIZE; i++) {
> +			struct page *page;
> +
> +			page = pfn_to_page(pfn_t_to_pfn(pfn) + i);
> +			if (page->mapping)
> +				continue;
> +			page->mapping = filp->f_mapping;
> +		}
> +	}
>  	dax_read_unlock(id);
>  
>  	return rc;
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR