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    Subject[PATCH 4.19 168/639] drm/xen-front: Fix mmap attributes for display buffers
    Date
    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-andr2000@gmail.com
    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 c85bfe7571cbf..802662839e7ed 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,
    --
    2.20.1


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