Re: [PATCH] drm/vma-manager: Don't unmap COW'd pages when zapping bo ptes

[Thomas Hellstrom <thellstrom@vmware.com>]

On 11/20/2013 11:14 AM, David Herrmann wrote:
> Hi
>
> On Wed, Nov 20, 2013 at 10:55 AM, Thomas Hellstrom
> <thellstrom@vmware.com> wrote:
>> Not sure if there are any user-space users of private bo mappings, but
>> if there are, or will be, zapping the COW'd pages when, for example,
>> moving a bo would confuse the user immensely since the net effect for the
>> user would be that pages written to would lose their contents.
> You're only talking about moving bos, but what happens when you evict
> a bo? You *must* clear COW mappings, too. Otherwise, they might still
> get read-access to the evicted bo.

Hmm. When I talk about COW'd pages, I mean individual anonymous pages.
If there is a COW mapping left in a VMA, it points to an anonymous page 
and will never access the evicted bo.
All (read-only-enabled) ptes pointing to the evicted bo would still be 
zapped, so I'm afraid I don't understand your comment?

>
> Note that we currently cause SIGBUS on access to mmap'd bos if they
> are evicted and cannot be restored (think: user-space mapped the
> VESA-FB but a real driver took over). So maybe we want two independent
> helpers here?
It shouldn't be needed.

Thanks,
Thomas


>
> Thanks
> David
>
>> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
>> ---
>>   include/drm/drm_vma_manager.h |    6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/drm/drm_vma_manager.h b/include/drm/drm_vma_manager.h
>> index c18a593..347077d 100644
>> --- a/include/drm/drm_vma_manager.h
>> +++ b/include/drm/drm_vma_manager.h
>> @@ -231,9 +231,9 @@ static inline void drm_vma_node_unmap(struct drm_vma_offset_node *node,
>>                                        struct address_space *file_mapping)
>>   {
>>          if (file_mapping && drm_vma_node_has_offset(node))
>> -               unmap_mapping_range(file_mapping,
>> -                                   drm_vma_node_offset_addr(node),
>> -                                   drm_vma_node_size(node) << PAGE_SHIFT, 1);
>> +               unmap_shared_mapping_range
>> +                       (file_mapping, drm_vma_node_offset_addr(node),
>> +                        drm_vma_node_size(node) << PAGE_SHIFT);
>>   }
>>
>>   /**
>> --
>> 1.7.10.4