On Thu, Mar 14, 2013 at 12:29:48PM +0100, Jan Kiszka wrote:
> On 2013-03-14 11:15, Jan Kiszka wrote:
> >>>
> >>> - if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED)) {
> >>> - pr_debug("vcpu %d received sipi with vector # %x\n",
> >>> - vcpu->vcpu_id, vcpu->arch.sipi_vector);
> >>> - kvm_lapic_reset(vcpu);
> >>> - kvm_vcpu_reset(vcpu);
> >>> - vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
> >>> - }
> >>> -
> >>> vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
> >>> r = vapic_enter(vcpu);
> >>
> >> vmx_vcpu_reset overwrites vcpu->srcu_idx if ->vcpu_reset is called from
> >> within srcu section.
> >
> > Indeed.
> >
> > Do you know what the look over vmx_set_cr0 actually protects?
>
> Found it: It's not actually protecting anything. enter_rmode is called,
> and that assumes that lock to be held. If enter_rmode faces an
> uninitialized tss, it drops the lock before calling vmx_set_tss_addr.
>
> Well, I wonder if that is a good place to fix the TSS issue. Why not
> make that special case (lacking KVM_SET_TSS_ADDR before first KVM_RUN) a
> static jump key and check for it on KVM_RUN?
>
Or finally break userspace that does not set it before calling kvm_run.
I haven't seen people complain about "kvm: KVM_SET_TSS_ADDR need to be
called before entering vcpu" warning in dmesg. Or create TSS mem slot at
0xfeffd000 during VM creation and destroy it if userspace overwrites it.
--
Gleb.
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