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    SubjectRe: [PATCH] drm: make sure page protections are updated after changing vm_flags.
    On 10/06/09 13:39, Andrew Morton wrote:
    > On Wed, 30 Sep 2009 15:55:39 -0700
    > Jeremy Fitzhardinge <jeremy@goop.org> wrote:
    >
    >
    >> Some architectures compute ->vm_page_prot depending on ->vm_flags, so
    >> we need to update the protections after adjusting the flags.
    >>
    >> Reported-by: Jan Beulich <JBeulich@novell.com>
    >> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    >>
    >> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
    >> index 8104eca..9d3e39f 100644
    >> --- a/drivers/gpu/drm/drm_gem.c
    >> +++ b/drivers/gpu/drm/drm_gem.c
    >> @@ -537,7 +537,7 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
    >> vma->vm_ops = obj->dev->driver->gem_vm_ops;
    >> vma->vm_private_data = map->handle;
    >> /* FIXME: use pgprot_writecombine when available */
    >> - vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
    >> + vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
    >>
    >> /* Take a ref for this mapping of the object, so that the fault
    >> * handler can dereference the mmap offset's pointer to the object.
    >>
    > u fail changelogology.
    >
    > What were the consequences of the bug which you just fixed?
    >

    AFAIK this only affects running X under Xen; without this patch you get
    lots of coloured blobs on the screen, or maybe a complete lockup. Or
    anything really.

    But that still depends on lots of out-of-tree stuff, so I don't think
    there are any consequences for anyone else. But it is wrong in principle.

    J


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