On 11/20/2013 03:24 PM, Daniel Vetter wrote:
On Wed, Nov 20, 2013 at 01:55:49AM -0800, Thomas Hellstrom 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.
Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Presuming I'm not horribly confused about that all the vm slang in the
kerneldoc means this changes is
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Now I still hold that userspace creating anynomous bo mappings is rather
crazy, but meh ;-) I guess the real question is whether we have anyone
relying on this out there (or planing to), in which case we either need to
funnel this through stable kernels or whack a drm feature flag onto
drivers/kernels with this fixed. But I seriously hope the answer is no.
Cheers, Daniel
Thanks for reviewing. I don't think there's a need to take this through
stable, since I don't know of anyone using private VMAs,
Actually I'll need to hold off on this for a while since on some archs
this may cause
ptes of shared pages to not be zapped. If the arch doesn't have
PTE_SPECIAL, shared pages on MIXEDMAP vmas will come through as
vm_normal_page, and since page->mapping is usually (un)set to NULL by
our drivers, this will result in false positives for COW'ed pages.
So that test is buggy, or us not setting page->mapping to the mapping we
use is buggy. It's too late in the day to decide which.
/Thomas
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