On 02/15/2012 09:36 PM, Andy Lutomirski wrote: > Hi, kvm people- > > Here's a strange failure. It could be a bug in something > RHEL6-specific, but it could be a generic issue that only triggers > with a paravirt guest with old userspace on a non-ept host. There was > a bug like this on Xen, and I'm wondering something's wrong on kvm as > well. > > For background, a change in 3.1 (IIRC) means that, when > vsyscall=emulate or vsyscall=none, the vsyscall page in the fixmap is > NX. It seems like Amit's machine is marking the physical PTE present > but unreadable.
No such thing as present and unreadable, without EPT. > So I could have messed up, or there could be a subtle > bug somewhere. Any ideas? What's the code trying to do? Execute an instruction from an non-executable page, trap the #PF, and emulate? And what are the symptoms? wrong error code for the #PF? That could easily be a kvm bug. > > I'll try to reproduce on a non-ept host later on, but that will > involve finding one. rmmod kvm-intel moprobe kvm-intel ept=0 > Hmm. You don't have ept. If your guest kernel supports paravirt, > then you might use the hypercall interface instead of programming the > fixmap directly. There is no hypercall interface for writing page tables in kvm. > > > > > This is what I get with vsyscall=none, where emulate and native work > > fine on the 3.2 kernel on different host hardware, the guest stays the > > same: > > > > > > [ 2.874661] debug: unmapping init memory > > ffffffff8167f000..ffffffff818dc000 > > [ 2.876778] Write protecting the kernel read-only data: 6144k > > [ 2.879111] debug: unmapping init memory > > ffff880001318000..ffff880001400000 > > [ 2.881242] debug: unmapping init memory > > ffff8800015a0000..ffff880001600000 > > [ 2.884637] init[1] vsyscall attempted with vsyscall=none > > ip:ffffffffff600400 cs:33 sp:7fff2f48fe18 ax:7fff2f48fe50 si:7fff2f48ff08 > > di:0 > > This like (vsyscall attempted) means that the emulation worked > correctly. Your other traces didn't have it or anything like it, > which mostly rules out do_emulate_vsyscall issues. > Can you point me at the code in question? Amit, a trace would be nice. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
