On 2014-06-29 16:32, Jan Kiszka wrote: > On 2014-06-29 16:27, Gleb Natapov wrote: >> On Sun, Jun 29, 2014 at 04:01:04PM +0200, Borislav Petkov wrote: >>> On Sun, Jun 29, 2014 at 04:42:47PM +0300, Gleb Natapov wrote: >>>> Please do so and let us know. >>> >>> Yep, just did. Reverting ae9fedc793 fixes the issue. >>> >>>> reinj:1 means that previous injection failed due to another #PF that >>>> happened during the event injection itself This may happen if GDT or fist >>>> instruction of a fault handler is not mapped by shadow pages, but here >>>> it says that the new page fault is at the same address as the previous >>>> one as if GDT is or #PF handler is mapped there. Strange. Especially >>>> since #DF is injected successfully, so GDT should be fine. May be wrong >>>> cpl makes svm crazy? >>> >>> Well, I'm not going to even pretend to know kvm to know *when* we're >>> saving VMCB state but if we're saving the wrong CPL and then doing the >>> pagetable walk, I can very well imagine if the walker gets confused. One >>> possible issue could be U/S bit (bit 2) in the PTE bits which allows >>> access to supervisor pages only when CPL < 3. I.e., CPL has effect on >>> pagetable walk and a wrong CPL level could break it. >>> >>> All a conjecture though... >>> >> Looks plausible, still strange that second #PF is at the same address as the first one though. >> Anyway, not we have the commit to blame. > > I suspect there is a gap between cause and effect. I'm tracing CPL > changes currently, and my first impression is that QEMU triggers an > unwanted switch from CPL 3 to 0 on vmport access: > > qemu-system-x86-11883 [001] 7493.378630: kvm_entry: vcpu 0 > qemu-system-x86-11883 [001] 7493.378631: bprint: svm_vcpu_run: entry cpl 0 > qemu-system-x86-11883 [001] 7493.378636: bprint: svm_vcpu_run: exit cpl 3 > qemu-system-x86-11883 [001] 7493.378637: kvm_exit: reason io rip 0x400854 info 56580241 400855 > qemu-system-x86-11883 [001] 7493.378640: kvm_emulate_insn: 0:400854:ed (prot64) > qemu-system-x86-11883 [001] 7493.378642: kvm_userspace_exit: reason KVM_EXIT_IO (2) > qemu-system-x86-11883 [001] 7493.378655: bprint: kvm_arch_vcpu_ioctl_get_sregs: ss.dpl 0 > qemu-system-x86-11883 [001] 7493.378684: bprint: kvm_arch_vcpu_ioctl_set_sregs: ss.dpl 0 > qemu-system-x86-11883 [001] 7493.378685: bprint: svm_set_segment: cpl = 0 > qemu-system-x86-11883 [001] 7493.378711: kvm_pio: pio_read at 0x5658 size 4 count 1 val 0x3442554a > > Yeah... do we have to manually sync save.cpl into ss.dpl on get_sregs > on AMD? > Applying this logic: diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index ec8366c..b5e994a 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1462,6 +1462,7 @@ static void svm_get_segment(struct kvm_vcpu *vcpu, */ if (var->unusable) var->db = 0; + var->dpl = to_svm(vcpu)->vmcb->save.cpl; break; } } ...and my VM runs smoothly so far. Does it make sense in all scenarios? Jan
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