Bandan Das <b...@redhat.com> wrote: > Nadav Amit <nadav.a...@gmail.com> writes: > >> Jan Kiszka <jan.kis...@siemens.com> wrote: >> >>> On 2015-04-08 19:40, Nadav Amit wrote: >>>> Jan Kiszka <jan.kis...@siemens.com> wrote: >>>> >>>>> On 2015-04-08 18:59, Nadav Amit wrote: >>>>>> Jan Kiszka <jan.kis...@siemens.com> wrote: >>>>>> >>>>>>> On 2015-04-08 18:40, Nadav Amit wrote: >>>>>>>> Hi, >>>>>>>> >>>>>>>> I would appreciate if someone explains the reason for enabling LINT0 >>>>>>>> during >>>>>>>> APIC reset. This does not correspond with Intel SDM Figure 10-8: “Local >>>>>>>> Vector Table” that says all LVT registers are reset to 0x10000. >>>>>>>> >>>>>>>> In kvm_lapic_reset, I see: >>>>>>>> >>>>>>>> apic_set_reg(apic, APIC_LVT0, >>>>>>>> SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT)); >>>>>>>> >>>>>>>> Which is actually pretty similar to QEMU’s apic_reset_common: >>>>>>>> >>>>>>>> if (bsp) { >>>>>>>> /* >>>>>>>> * LINT0 delivery mode on CPU #0 is set to ExtInt at initialization >>>>>>>> * time typically by BIOS, so PIC interrupt can be delivered to the >>>>>>>> * processor when local APIC is enabled. >>>>>>>> */ >>>>>>>> s->lvt[APIC_LVT_LINT0] = 0x700; >>>>>>>> } >>>>>>>> >>>>>>>> Yet, in both cases, I miss the point - if it is typically done by the >>>>>>>> BIOS, >>>>>>>> why does QEMU or KVM enable it? >>>>>>>> >>>>>>>> BTW: KVM seems to run fine without it, and I think setting it causes me >>>>>>>> problems in certain cases. >>>>>>> >>>>>>> I suspect it has some historic BIOS backgrounds. Already tried to find >>>>>>> more information in the git logs of both code bases? Or something that >>>>>>> indicates of SeaBIOS or BochsBIOS once didn't do this initialization? >>>>>> Thanks. I found no indication of such thing. >>>>>> >>>>>> QEMU’s commit message (0e21e12bb311c4c1095d0269dc2ef81196ccb60a) says: >>>>>> >>>>>> Don't route PIC interrupts through the local APIC if the local APIC >>>>>> config says so. By Ari Kivity. >>>>>> >>>>>> Maybe Avi Kivity knows this guy. >>>>> >>>>> ths? That should have been Thiemo Seufer (IIRC), but he just committed >>>>> the code back then (and is no longer with us, sadly). >>>> Oh… I am sorry - I didn’t know about that.. (I tried to make an unfunny >>>> joke >>>> about Avi knowing “Ari”). >>> >>> Ah. No problem. My brain apparently fixed that typo up unnoticed. >>> >>>>> But if that commit went in without any BIOS changes around it, QEMU >>>>> simply had to do the job of the latter to keep things working. >>>> So should I leave it as is? Can I at least disable in KVM during INIT (and >>>> leave it as is for RESET)? >>> >>> No, I don't think there is a need to leave this inaccurate for QEMU if >>> our included BIOS gets it right. I don't know what the backward >>> bug-compatibility of KVM is, though. Maybe you can identify since when >>> our BIOS is fine so that we can discuss time frames. >> >> I think that it was addressed in commit >> 19c1a7692bf65fc40e56f93ad00cc3eefaad22a4 ("Initialize the LINT LVTs on the >> local APIC of the BSP.”) So it should be included in seabios 0.5.0, which >> means qemu 0.12 - so we are talking about the end of 2009 or start of 2010. > > The probability that someone will use a newer version of kernel with something > as old as 0.12 is probably minimal. I think it's ok to change it with a > comment > indicating the reason. To be on the safe side, however, a user changeable > switch > is something worth considering.
I don’t see any existing mechanism for KVM to be aware of its user type and version. I do see another case of KVM hacks that are intended for fixing very old QEMU bugs (see 3a624e29c75 changes in vmx_set_segment, which are from pretty much the same time-frame of the issue I try to fix). Since this is something which would follow around, please advise what would be the format. A new ioctl that would supply the userspace “type” (according to predefined constants) and version? Thanks, Nadav-- 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