On Thu, Mar 14, 2013 at 01:16:41PM +0100, Jan Kiszka wrote:
> On 2013-03-14 13:12, Gleb Natapov wrote:
> > 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.
>
> Whatever is preferred, I'm not able to decide (about ABI "breakage"
> specifically). I just think any of them would be better than pulling
> vcpu_reset out of the inner loop again just to fulfill the locking
> requirements.
>
I agree. Lets try second approach. Can you write a patch?
--
Gleb.
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