Re: [PATCH v6 09/10] device-dax: set mapping prior to vmf_insert_pfn{,_pmd,pud}()

[Joao Martins <joao.m.martins@xxxxxxxxxx>]

On 11/24/21 19:10, Joao Martins wrote:
> Normally, the @page mapping is set prior to inserting the page into a
> page table entry. Make device-dax adhere to the same ordering, rather
> than setting mapping after the PTE is inserted.
> 
> The address_space never changes and it is always associated with the
> same inode and underlying pages. So, the page mapping is set once but
> cleared when the struct pages are removed/freed (i.e. after
> {devm_}memunmap_pages()).
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
> ---
>  drivers/dax/device.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 9c87927d4bc2..0ef9fecec005 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -121,6 +121,8 @@ static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
>  
>  	*pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);
>  
> +	dax_set_mapping(vmf, *pfn, fault_size);
> +
>  	return vmf_insert_mixed(vmf->vma, vmf->address, *pfn);
>  }
>  
> @@ -161,6 +163,8 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
>  
>  	*pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);
>  
> +	dax_set_mapping(vmf, *pfn, fault_size);
> +
>  	return vmf_insert_pfn_pmd(vmf, *pfn, vmf->flags & FAULT_FLAG_WRITE);
>  }
>  
> @@ -203,6 +207,8 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
>  
>  	*pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);
>  
> +	dax_set_mapping(vmf, *pfn, fault_size);
> +
>  	return vmf_insert_pfn_pud(vmf, *pfn, vmf->flags & FAULT_FLAG_WRITE);
>  }
>  #else
> @@ -245,8 +251,6 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
>  		rc = VM_FAULT_SIGBUS;
>  	}
>  
> -	if (rc == VM_FAULT_NOPAGE)
> -		dax_set_mapping(vmf, pfn, fault_size);
>  	dax_read_unlock(id);
>  
>  	return rc;
> 
This last chunk is going to spoof out a new warning because @fault_size in
dev_dax_huge_fault stops being used after this patch.
I've added below chunk for the next version (in addition to Christoph comments in
patch 4):

@@ -217,7 +223,6 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
                enum page_entry_size pe_size)
 {
        struct file *filp = vmf->vma->vm_file;
-       unsigned long fault_size;
        vm_fault_t rc = VM_FAULT_SIGBUS;
        int id;
        pfn_t pfn;
@@ -230,23 +235,18 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
        id = dax_read_lock();
        switch (pe_size) {
        case PE_SIZE_PTE:
-               fault_size = PAGE_SIZE;
                rc = __dev_dax_pte_fault(dev_dax, vmf, &pfn);
                break;
        case PE_SIZE_PMD:
-               fault_size = PMD_SIZE;
                rc = __dev_dax_pmd_fault(dev_dax, vmf, &pfn);
                break;
        case PE_SIZE_PUD:
-               fault_size = PUD_SIZE;
                rc = __dev_dax_pud_fault(dev_dax, vmf, &pfn);
                break;
        default:
                rc = VM_FAULT_SIGBUS;
        }