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Subject[Xen-devel][PATCH] drm/xen-front: Fix mmap attributes for display buffers
Date
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);

/*
* vm_operations_struct.fault handler will be called if CPU access
@@ -283,7 +282,7 @@ void *xen_drm_front_gem_prime_vmap(struct drm_gem_object *gem_obj)
return NULL;

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,
--
2.20.1
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