From: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com
[ Upstream commit 24ded292a5c2ed476f01c77fee65f8320552cd27 ]
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 Acked-by: Julien Grall julien.grall@arm.com Link: https://patchwork.freedesktop.org/patch/msgid/20190129150422.19867-1-andr200... Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/xen/xen_drm_front_gem.c | 13 ++++++++++--- 1 file changed, 10 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 c85bfe7571cb..802662839e7e 100644 --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c @@ -236,8 +236,14 @@ 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)); + /* + * 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);
/* * vm_operations_struct.fault handler will be called if CPU access @@ -283,8 +289,9 @@ void *xen_drm_front_gem_prime_vmap(struct drm_gem_object *gem_obj) if (!xen_obj->pages) return NULL;
+ /* Please see comment in gem_mmap_obj on mapping and attributes. */ return vmap(xen_obj->pages, xen_obj->num_pages, - VM_MAP, pgprot_writecombine(PAGE_KERNEL)); + VM_MAP, PAGE_KERNEL); }
void xen_drm_front_gem_prime_vunmap(struct drm_gem_object *gem_obj,