Messages in this thread | | | Subject | Re: WARNING in __mmdrop | From | Jason Wang <> | Date | Tue, 23 Jul 2019 11:55:28 +0800 |
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On 2019/7/22 下午4:02, Michael S. Tsirkin wrote: > On Mon, Jul 22, 2019 at 01:21:59PM +0800, Jason Wang wrote: >> On 2019/7/21 下午6:02, Michael S. Tsirkin wrote: >>> On Sat, Jul 20, 2019 at 03:08:00AM -0700, syzbot wrote: >>>> syzbot has bisected this bug to: >>>> >>>> commit 7f466032dc9e5a61217f22ea34b2df932786bbfc >>>> Author: Jason Wang <jasowang@redhat.com> >>>> Date: Fri May 24 08:12:18 2019 +0000 >>>> >>>> vhost: access vq metadata through kernel virtual address >>>> >>>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=149a8a20600000 >>>> start commit: 6d21a41b Add linux-next specific files for 20190718 >>>> git tree: linux-next >>>> final crash: https://syzkaller.appspot.com/x/report.txt?x=169a8a20600000 >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=129a8a20600000 >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=3430a151e1452331 >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=e58112d71f77113ddb7b >>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10139e68600000 >>>> >>>> Reported-by: syzbot+e58112d71f77113ddb7b@syzkaller.appspotmail.com >>>> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual >>>> address") >>>> >>>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection >>> OK I poked at this for a bit, I see several things that >>> we need to fix, though I'm not yet sure it's the reason for >>> the failures: >>> >>> >>> 1. mmu_notifier_register shouldn't be called from vhost_vring_set_num_addr >>> That's just a bad hack, >> >> This is used to avoid holding lock when checking whether the addresses are >> overlapped. Otherwise we need to take spinlock for each invalidation request >> even if it was the va range that is not interested for us. This will be very >> slow e.g during guest boot. > KVM seems to do exactly that. > I tried and guest does not seem to boot any slower. > Do you observe any slowdown?
Yes I do.
> > Now I took a hard look at the uaddr hackery it really makes > me nervious. So I think for this release we want something > safe, and optimizations on top. As an alternative revert the > optimization and try again for next merge window.
Will post a series of fixes, let me know if you're ok with that.
Thanks
> >
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