On 10/08/2013 04:55 PM, Jerome Glisse wrote:
On Tue, Oct 08, 2013 at 04:45:18PM +0200, Christian König wrote:
Am 08.10.2013 16:33, schrieb Jerome Glisse:
On Tue, Oct 08, 2013 at 04:14:40PM +0200, Maarten Lankhorst wrote:
Allocate and copy all kernel memory before doing reservations. This prevents a locking
inversion between mmap_sem and reservation_class, and allows us to drop the trylocking
in ttm_bo_vm_fault without upsetting lockdep.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
I would say NAK. Current code only allocate temporary page in AGP case.
So AGP case is userspace -> temp page -> cs checker -> radeon ib.
Non AGP is directly memcpy to radeon IB.
Your patch allocate memory memcpy userspace to it and it will then be
memcpy to IB. Which means you introduce an extra memcpy in the process
not something we want.
Totally agree. Additional to that there is no good reason to provide
anything else than anonymous system memory to the CS ioctl, so the
dependency between the mmap_sem and reservations are not really
clear to me.
Christian.
I think is that in other code path you take mmap_sem first then reserve
bo. But here we reserve bo and then we take mmap_sem because of copy
from user.
Cheers,
Jerome
Actually the log message is a little confusing. I think the mmap_sem
locking inversion problem is orthogonal to what's being fixed here.
This patch fixes the possible recursive bo::reserve caused by malicious
user-space handing a pointer to ttm memory so that the ttm fault handler
is called when bos are already reserved. That may cause a (possibly
interruptible) livelock.
Once that is fixed, we are free to choose the mmap_sem -> bo::reserve
locking order. Currently it's bo::reserve->mmap_sem(), but the hack
required in the ttm fault handler is admittedly a bit ugly. The plan is
to change the locking order to mmap_sem->bo::reserve
I'm not sure if it applies to this particular case, but it should be
possible to make sure that copy_from_user_inatomic() will always
succeed, by making sure the pages are present using get_user_pages(),
and release the pages after copy_from_user_inatomic() is done. That way
there's no need for a double memcpy slowpath, but if the copied data is
very fragmented I guess the resulting code may look ugly. The
get_user_pages() function will return an error if it hits TTM pages.
/Thomas
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