On Mon, Mar 11, 2013 at 07:47:03PM +0100, Jan Kiszka wrote: > On 2013-03-11 19:39, Gleb Natapov wrote: > > On Mon, Mar 11, 2013 at 07:27:44PM +0100, Jan Kiszka wrote: > >> On 2013-03-11 19:13, Gleb Natapov wrote: > >>> On Mon, Mar 11, 2013 at 07:05:48PM +0100, Jan Kiszka wrote: > >>>> On 2013-03-11 18:41, Gleb Natapov wrote: > >>>>> On Mon, Mar 11, 2013 at 06:34:03PM +0100, Jan Kiszka wrote: > >>>>>> On 2013-03-11 18:23, Gleb Natapov wrote: > >>>>>>> On Mon, Mar 11, 2013 at 04:36:33PM +0100, Jan Kiszka wrote: > >>>>>>>> On 2013-03-11 15:23, Paolo Bonzini wrote: > >>>>>>>>> Il 11/03/2013 15:05, Gleb Natapov ha scritto: > >>>>>>>>>> On Mon, Mar 11, 2013 at 03:01:40PM +0100, Jan Kiszka wrote: > >>>>>>>>>>>> We are not moving away from mp_state, we are moving away from using > >>>>>>>>>>>> mp_state for signaling because with nested virt INIT does not always > >>>>>>>>>>>> change mp_state, not only that it can change mp_state long after signal > >>>>>>>>>>>> is received after vmx off is done. > >>>>>>>>>>> > >>>>>>>>>>> Right. > >>>>>>>>>>> > >>>>>>>>>>> BTW, for that to happen, we will also need to influence the INIT level. > >>>>>>>>>>> Unless I misread the spec, INIT is blocked while in root mode, and if > >>>>>>>>>>> you deassert INIT before leaving root (vmxoff, vmenter), nothing > >>>>>>>>>>> actually happens. So what matters is the INIT signal level at the exit > >>>>>>>>>>> of root mode. > >>>>>>>>>>> > >>>>>>>>>> You are talking about INIT# signal received via CPU pin, right? I think > >>>>>>>>>> INIT send by IPI cannot go away. > >>>>>>>>> > >>>>>>>>> Neither can go away. For INIT sent by IPI, 10.4.7 says: > >>>>>>>>> > >>>>>>>>> Only the Pentium and P6 family processors support the INIT-deassert IPI. > >>>>>>>>> An INIT-disassert IPI has no affect on the state of the APIC, other than > >>>>>>>>> to reload the arbitration ID register with the value in the APIC ID > >>>>>>>>> register. > >>>>>>>>> > >>>>>>>>> 18.27.1 also says that "In the local APIC, NMI and INIT (except for INIT > >>>>>>>>> deassert) are always treated as edge triggered interrupts". > >>>>>>>>> > >>>>>>>>> > >>>>>>>>> For INIT#, the ICH9 chipset says that "INIT# is driven low for 16 PCI > >>>>>>>>> clocks" when a soft reset is requested. So we can guess that INIT# is > >>>>>>>>> also edge-triggered. > >>>>>>>> > >>>>>>>> Ah, ok. So, virtually, INIT stays asserted until it can be delivered in > >>>>>>>> form of a reset or a vmexit. > >>>>>>>> > >>>>>>> vmexit clears it? > >>>>>> > >>>>>> It has to. Otherwise, it would hit the host on vmxoff. > >>>>>> > >>>>> Why do you thing this is not happening? > >>>>> > >>>>> Look at [1] page 10 "VMX and INIT blocking". Do you think they were > >>>>> lucky to hit CPU while it was in a root mode? > >>>>> > >>>>> [1] http://www.invisiblethingslab.com/resources/2011/Software%20Attacks%20on%20Intel%20VT-d.pdf > >>>> > >>>> Interesting. And confusing. If a VMM cannot "consume" INIT events by > >>>> reentering the guest nor postpone those events up to that point if they > >>>> arrived in root mode, the whole vmexit-on-INIT thing is practically > >>>> useless. I wonder what use case Intel had in mind while designing this. > >>>> > >>> I actually find it very useful. On INIT vmexit hypervisor may call > >>> vmxoff and do proper reset. I find it less useful on AMD where you need > >>> to send self INIT IPI, but then how you can send self SIPI? > >> > >> Where's the difference? On Intel, SIPI is also not deliverable until > >> after vmxoff. So that signal has to come from the INIT sender, just like > >> on AMD. > >> > > On Intel: > > CPU 1 CPU 2 in a guest mode > > send INIT > > send SIPI > > INIT vmexit > > vmxoff > > reset and start from SIPI vector > > Is SIPI sticky as well, even if the CPU is not in the wait-for-SIPI > state (but runnable and in vmxon) while receiving it? > That what they seams to be saying: However, an INIT and SIPI interrupts sent to a CPU during time when it is in a VMX mode are remembered and delivered, perhaps hours later, when the CPU exits the VMX mode Otherwise their exploit will not work. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
