On Tue 03-12-19 11:48:53, Thomas Hellström (VMware) wrote:
> From: Thomas Hellstrom <thellst...@vmware.com>
> 
> TTM graphics buffer objects may, transparently to user-space,  move
> between IO and system memory. When that happens, all PTEs pointing to the
> old location are zapped before the move and then faulted in again if
> needed. When that happens, the page protection caching mode- and
> encryption bits may change and be different from those of
> struct vm_area_struct::vm_page_prot.
> 
> We were using an ugly hack to set the page protection correctly.
> Fix that and instead use vmf_insert_mixed_prot() and / or
> vmf_insert_pfn_prot().
> Also get the default page protection from
> struct vm_area_struct::vm_page_prot rather than using vm_get_page_prot().
> This way we catch modifications done by the vm system for drivers that
> want write-notification.

So essentially this should have any new side effect on functionality it
is just making a hacky/ugly code less so? In other words what are the
consequences of having page protection inconsistent from vma's?

> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Michal Hocko <mho...@suse.com>
> Cc: "Matthew Wilcox (Oracle)" <wi...@infradead.org>
> Cc: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
> Cc: Ralph Campbell <rcampb...@nvidia.com>
> Cc: "Jérôme Glisse" <jgli...@redhat.com>
> Cc: "Christian König" <christian.koe...@amd.com>
> Signed-off-by: Thomas Hellstrom <thellst...@vmware.com>
> Reviewed-by: Christian König <christian.koe...@amd.com>
> ---
>  drivers/gpu/drm/ttm/ttm_bo_vm.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index e6495ca2630b..2098f8d4dfc5 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -173,7 +173,6 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>                                   pgoff_t num_prefault)
>  {
>       struct vm_area_struct *vma = vmf->vma;
> -     struct vm_area_struct cvma = *vma;
>       struct ttm_buffer_object *bo = vma->vm_private_data;
>       struct ttm_bo_device *bdev = bo->bdev;
>       unsigned long page_offset;
> @@ -244,7 +243,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>               goto out_io_unlock;
>       }
>  
> -     cvma.vm_page_prot = ttm_io_prot(bo->mem.placement, prot);
> +     prot = ttm_io_prot(bo->mem.placement, prot);
>       if (!bo->mem.bus.is_iomem) {
>               struct ttm_operation_ctx ctx = {
>                       .interruptible = false,
> @@ -260,7 +259,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>               }
>       } else {
>               /* Iomem should not be marked encrypted */
> -             cvma.vm_page_prot = pgprot_decrypted(cvma.vm_page_prot);
> +             prot = pgprot_decrypted(prot);
>       }
>  
>       /*
> @@ -284,10 +283,11 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault 
> *vmf,
>               }
>  
>               if (vma->vm_flags & VM_MIXEDMAP)
> -                     ret = vmf_insert_mixed(&cvma, address,
> -                                     __pfn_to_pfn_t(pfn, PFN_DEV));
> +                     ret = vmf_insert_mixed_prot(vma, address,
> +                                                 __pfn_to_pfn_t(pfn, 
> PFN_DEV),
> +                                                 prot);
>               else
> -                     ret = vmf_insert_pfn(&cvma, address, pfn);
> +                     ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
>  
>               /* Never error on prefaulted PTEs */
>               if (unlikely((ret & VM_FAULT_ERROR))) {
> @@ -319,7 +319,7 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
>       if (ret)
>               return ret;
>  
> -     prot = vm_get_page_prot(vma->vm_flags);
> +     prot = vma->vm_page_prot;
>       ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
>       if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
>               return ret;
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs
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