On 1/30/19 11:09 AM, Oleksandr Andrushchenko wrote:
On 1/29/19 9:07 PM, Julien Grall wrote:
Hi Oleksandr,
On 1/29/19 3:04 PM, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com
When GEM backing storage is allocated those are normal pages, so there is no point using pgprot_writecombine while mmaping. This fixes mismatch of buffer pages' memory attributes between the frontend and backend which may cause screen artifacts.
Fixes: c575b7eeb89f ("drm/xen-front: Add support for Xen PV display frontend")
Signed-off-by: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Suggested-by: Julien Grall julien.grall@arm.com
drivers/gpu/drm/xen/xen_drm_front_gem.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c index d303a2e17f5e..9d5c03d7668d 100644 --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c @@ -235,8 +235,7 @@ static int gem_mmap_obj(struct xen_gem_object *xen_obj, vma->vm_flags &= ~VM_PFNMAP; vma->vm_flags |= VM_MIXEDMAP; vma->vm_pgoff = 0; - vma->vm_page_prot =
- pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
+ vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
The patch looks good to me. It would be worth expanding the comment a bit before to explain that we overwrite vm_page_prot to use cacheable attribute as required by the Xen ABI.
Ok, then I'll put:
+ /* + * According to Xen on ARM ABI (xen/include/public/arch-arm.h): + * all memory which is shared with other entities in the system + * (including the hypervisor and other guests) must reside in memory + * which is mapped as Normal Inner Write-Back Outer Write-Back + * Inner-Shareable. + */ vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); Please let me know if this is not what you want
With the comment updated:
Acked-by: Julien Grall julien.grall@arm.com
If nobody objects I'll apply this to drm-misc-fixes next Monday
Cheers,
Thank you, Oleksandr