On Sun, Aug 04, 2013 at 06:42:09PM +0200, Jan Kiszka wrote:
> On 2013-08-04 18:15, Xiao Guangrong wrote:
> >
> > On Aug 4, 2013, at 11:14 PM, Jan Kiszka <jan.kiszka@xxxxxx> wrote:
> >
> >> On 2013-08-04 15:44, Gleb Natapov wrote:
> >>> On Sun, Aug 04, 2013 at 12:53:56PM +0300, Gleb Natapov wrote:
> >>>> On Sun, Aug 04, 2013 at 12:32:06PM +0300, Gleb Natapov wrote:
> >>>>> On Sun, Aug 04, 2013 at 11:24:41AM +0200, Jan Kiszka wrote:
> >>>>>> On 2013-08-01 16:08, Gleb Natapov wrote:
> >>>>>>> Another day -- another version of the nested EPT patches. In this version
> >>>>>>> included fix for need_remote_flush() with shadowed ept, set bits 6:8
> >>>>>>> of exit_qualification during ept_violation, update_permission_bitmask()
> >>>>>>> made to work with shadowed ept pages and other small adjustment according
> >>>>>>> to review comments.
> >>>>>>
> >>>>>> Was just testing it here and ran into a bug: I've L2 accessing the HPET
> >>>>>> MMIO region that my L1 passed through from L0 (where it is supposed to
> >>>>>> be emulated in this setup). This used to work with an older posting of
> >>>>> Not sure I understand your setup. L0 emulates HPET, L1 passes it through
> >>>>> to L2 (mmaps it and creates kvm slot that points to it) and when L2
> >>>>> accessed it it locks up?
> >>>>>
> >>>>>> Jun, but now it locks up (infinite loop over L2's MMIO access, no L2->L1
> >>>>>> transition). Any ideas where to look for debugging this?
> >>>>>>
> >>>>> Can you do an ftrace -e kvm -e kvmmmu? Unit test will also be helpful :)
> >>>>>
> >>>> I did an MMIO access from nested guest in the vmx unit test (which is
> >>>> naturally passed through to L0 since L1 is so simple) and I can see that
> >>>> the access hits L0.
> >>>>
> >>> But then unit test not yet uses nested EPT :)
> >>
> >> Indeed, that's what I was about to notice as well. EPT test cases are on
> >> Arthur's list, but I suggested to start easier with some MSR switches
> >> (just to let him run into KVM's PAT bugs ;) ).
> >>
> >> Anyway, here are the traces:
> >>
> >> qemu-system-x86-11521 [000] 4724.170191: kvm_entry: vcpu 0
> >> qemu-system-x86-11521 [000] 4724.170192: kvm_exit: reason EPT_VIOLATION rip 0xffffffff8102ab70 info 181 0
> >> qemu-system-x86-11521 [000] 4724.170192: kvm_page_fault: address 1901978 error_code 181
> >> qemu-system-x86-11521 [000] 4724.170193: kvm_mmu_pagetable_walk: addr 1901978 pferr 0
> >> qemu-system-x86-11521 [000] 4724.170193: kvm_mmu_paging_element: pte 3c04c007 level 4
> >> qemu-system-x86-11521 [000] 4724.170193: kvm_mmu_paging_element: pte 3c04d007 level 3
> >> qemu-system-x86-11521 [000] 4724.170193: kvm_mmu_paging_element: pte 3c05a007 level 2
> >> qemu-system-x86-11521 [000] 4724.170193: kvm_mmu_paging_element: pte 1901037 level 1
> >> qemu-system-x86-11521 [000] 4724.170197: kvm_entry: vcpu 0
> >> qemu-system-x86-11521 [000] 4724.170198: kvm_exit: reason EPT_VIOLATION rip 0xffffffff8102ab77 info 81 0
> >> qemu-system-x86-11521 [000] 4724.170199: kvm_page_fault: address 3a029000 error_code 81
> >> qemu-system-x86-11521 [000] 4724.170199: kvm_mmu_pagetable_walk: addr 3a029000 pferr 0
> >> qemu-system-x86-11521 [000] 4724.170199: kvm_mmu_paging_element: pte 3c04c007 level 4
> >> qemu-system-x86-11521 [000] 4724.170199: kvm_mmu_paging_element: pte 3c04d007 level 3
> >> qemu-system-x86-11521 [000] 4724.170199: kvm_mmu_paging_element: pte 3c21e007 level 2
> >> qemu-system-x86-11521 [000] 4724.170200: kvm_mmu_paging_element: pte 3a029037 level 1
> >> qemu-system-x86-11521 [000] 4724.170203: kvm_entry: vcpu 0
> >> qemu-system-x86-11521 [000] 4724.170204: kvm_exit: reason EPT_VIOLATION rip 0xffffffff8102ab77 info 181 0
> >> qemu-system-x86-11521 [000] 4724.170204: kvm_page_fault: address fed000f0 error_code 181
> >> qemu-system-x86-11521 [000] 4724.170205: kvm_mmu_pagetable_walk: addr fed000f0 pferr 0
> >> qemu-system-x86-11521 [000] 4724.170205: kvm_mmu_paging_element: pte 3c04c007 level 4
> >> qemu-system-x86-11521 [000] 4724.170205: kvm_mmu_paging_element: pte 3c42f003 level 3
> >> qemu-system-x86-11521 [000] 4724.170205: kvm_mmu_paging_element: pte 3c626003 level 2
> >> qemu-system-x86-11521 [000] 4724.170206: kvm_mmu_paging_element: pte fed00033 level 1
> >> qemu-system-x86-11521 [000] 4724.170213: mark_mmio_spte: sptep:0xffff88014e8ad800 gfn fed00 access 6 gen b7f
> >> qemu-system-x86-11521 [000] 4724.170214: kvm_mmu_pagetable_walk: addr ffffffff8102ab77 pferr 10 F
> >> qemu-system-x86-11521 [000] 4724.170215: kvm_mmu_pagetable_walk: addr 1710000 pferr 6 W|U
> >> qemu-system-x86-11521 [000] 4724.170215: kvm_mmu_paging_element: pte 3c04c007 level 4
> >> qemu-system-x86-11521 [000] 4724.170215: kvm_mmu_paging_element: pte 3c04d007 level 3
> >> qemu-system-x86-11521 [000] 4724.170216: kvm_mmu_paging_element: pte 3c059007 level 2
> >> qemu-system-x86-11521 [000] 4724.170216: kvm_mmu_paging_element: pte 1710037 level 1
> >> qemu-system-x86-11521 [000] 4724.170216: kvm_mmu_paging_element: pte 1711067 level 4
> >> qemu-system-x86-11521 [000] 4724.170216: kvm_mmu_walker_error: pferr 19 P|RSVD|F
> >
> > I guess the bug is here, could you please change this code to:
> >
> > - if (unlikely(is_rsvd_bits_set(&vcpu->arch.mmu, pte,
> > + if (unlikely(is_rsvd_bits_set(mmu, pte,
> > walker->level))) {
> >
> > (
> > In static int FNAME(walk_addr_generic)(struct guest_walker *walker,
> > struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> > gva_t addr, u32 access)
> > )
> >
> > and try again?
> >
>
> Thanks, that fixed the bug!
>
Awesome!
> Obviously, previous version were less strict or imprecise with reserved
> bit checking as this pattern exists in the version that worked here as well.
>
Previous version did not use mmu->rsvd_bits_mask for nEPT reserved bit
checking so is_rsvd_bits_set() happened to work correctly for nested mmu
using non nested mmu pointer, but when I change it to use
mmu->rsvd_bits_mask the bug become triggerable. In theory this bug
should be triggerable on nested SVM to if two levels of paging use
different modes, no?
--
Gleb.
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