On Thu, 15 Aug 2019 09:00:06 -0700 Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > On Thu, Aug 15, 2019 at 09:23:24AM -0600, Alex Williamson wrote: > > Ok, fun day of trying to figure out which ranges are relevant, I've > > narrowed it down to all of these: > > > > 0xffe00 > > 0xfee00 > > 0xfec00 > > APIC and I/O APIC stuff > > > 0xc1000 > > Assigned audio > > > 0x80a000 > > ? > > > 0x800000 > > GPU BAR > > > 0x100000 > > ? > > The APIC ranges are puzzling, I wouldn't expect their mappings to change. > > > ie. I can effective only say that sp->gfn values of 0x0, 0x40000, and > > 0x80000 can take the continue branch without seeing bad behavior in the > > VM. > > > > The assigned GPU has BARs at GPAs: > > > > 0xc0000000-0xc0ffffff > > 0x800000000-0x808000000 > > 0x808000000-0x809ffffff > > > > And the assigned companion audio function is at GPA: > > > > 0xc1080000-0xc1083fff > > > > Only one of those seems to align very well with a gfn base involved > > here. The virtio ethernet has an mmio range at GPA 0x80a000000, > > otherwise I don't find any other I/O devices coincident with the gfns > > above. > > > > I'm running the VM with 2MB hugepages, but I believe the issue still > > occurs with standard pages. When run with standard pages I see more > > hits to gfn values 0, 0x40000, 0x80000, but the same number of hits to > > the set above that cannot take the continue branch. I don't know if > > that means anything. > > > > Any further ideas what to look for? Thanks, > > Maybe try isolating which memslot removal causes problems? E.g. flush > the affected ranges if base_gfn == (xxx || yyy || zzz), otherwise flush > only the memslot's gfns. Based on the log you sent a while back for gfn > mismatches, I'm guessing the culprits are all GPU BARs, but it's > probably worth confirming. That might also explain why gfn == 0x80000 > can take the continue branch, i.e. if removing the corresponding memslot > is what's causing problems, then it's being flushed and not actually > taking the continue path. If I print out the memslot base_gfn, it seems pretty evident that only the assigned device mappings are triggering this branch. The base_gfns exclusively include: 0x800000 0x808000 0xc0089 Where the first two clearly match the 64bit BARs and the last is the result of a page that we need to emulate within the BAR @0xc0000000 at offset 0x88000, so the base_gfn is the remaining direct mapping. I don't know if this implies we're doing something wrong for assigned device slots, but maybe a more targeted workaround would be if we could specifically identify these slots, though there's no special registration of them versus other slots. Did you have any non-device assignment test cases that took this branch when developing the series? > One other thought would be to force a call to kvm_flush_remote_tlbs(kvm), > e.g. set flush=true just before the final kvm_mmu_remote_flush_or_zap(). > Maybe it's a case where there are no SPTEs for the memslot, but the TLB > flush is needed for some reason. This doesn't work. Thanks, Alex
