Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756725Ab3JHQrt (ORCPT ); Tue, 8 Oct 2013 12:47:49 -0400 Received: from mail-qa0-f41.google.com ([209.85.216.41]:44790 "EHLO mail-qa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754986Ab3JHQrq (ORCPT ); Tue, 8 Oct 2013 12:47:46 -0400 Date: Tue, 8 Oct 2013 12:47:38 -0400 From: Jerome Glisse To: Thomas Hellstrom Cc: Christian =?iso-8859-1?Q?K=F6nig?= , Maarten Lankhorst , Peter Zijlstra , Daniel Vetter , intel-gfx , Linux Kernel Mailing List , dri-devel , Alex Deucher , Thomas Gleixner , Ingo Molnar Subject: Re: [RFC PATCH] drm/radeon: fixup locking inversion between mmap_sem and reservations Message-ID: <20131008164737.GA2782@gmail.com> References: <5231E18D.7070306@canonical.com> <5231EF5A.7010901@vmware.com> <52323734.4070908@canonical.com> <5232A39B.5040205@vmware.com> <52541350.5060807@canonical.com> <20131008143354.GA2355@gmail.com> <52541A7E.6050807@vodafone.de> <20131008145540.GB2355@gmail.com> <525432EF.3050005@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <525432EF.3050005@vmware.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3033 Lines: 67 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 K?nig 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 > >>>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. Cheers, Jerome -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/