op 08-10-13 18:47, Jerome Glisse schreef: > On Tue, Oct 08, 2013 at 06:29:35PM +0200, Thomas Hellstrom wrote: >> 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 > get_user_pages + copy_from_user_inatomic is overkill. We should just > do get_user_pages which fails with ttm memory and then use copy_highpage > helper. I don't think we have to do anything that complicated, the easiest solution seems to be to call radeon_ib_get before calling radeon_cs_parser_relocs, and copy everything to the ib buffer before taking the reserve lock. ~Maarten _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
