On Tue, May 24, 2011, Tian, Kevin wrote about "RE: [PATCH 18/31] nVMX:
Implement VMLAUNCH and VMRESUME":
> > + /*
> > + * Switch from L1's VMCS (vmcs01), to L2's VMCS (vmcs02). Remember
> > + * vmcs01, on which CPU it was last loaded, and whether it was launched
> > + * (we need all these values next time we will use L1). Then recall
> > + * these values from the last time vmcs02 was used.
> > + */
> > + saved_vmcs02 = nested_get_current_vmcs02(vmx);
> > + if (!saved_vmcs02)
> > + return -ENOMEM;
> > +
> > + cpu = get_cpu();
> > + vmx->nested.saved_vmcs01.vmcs = vmx->vmcs;
> > + vmx->nested.saved_vmcs01.cpu = vcpu->cpu;
> > + vmx->nested.saved_vmcs01.launched = vmx->launched;
> > + vmx->vmcs = saved_vmcs02->vmcs;
> > + vcpu->cpu = saved_vmcs02->cpu;
>
> this may be another valid reason for your check on cpu_online in your
> latest [08/31] local_vcpus_link fix, since cpu may be offlined after
> this assignment. :-)
I believe that wrapping this part of the code with get_cpu()/put_cpu()
protected me from these kinds of race conditions.
By the way, please note that this part of the code was changed after my
latest loaded_vmcs overhaul. It now looks like this:
vmcs02 = nested_get_current_vmcs02(vmx);
if (!vmcs02)
return -ENOMEM;
cpu = get_cpu();
vmx->loaded_vmcs = vmcs02;
vmx_vcpu_put(vcpu);
vmx_vcpu_load(vcpu, cpu);
vcpu->cpu = cpu;
put_cpu();
(if Avi gives me the green light, I'll send the entire, up-to-date, patch set
again).
> > + vmcs12->launch_state = 1;
> > +
> > + prepare_vmcs02(vcpu, vmcs12);
>
> Since prepare_vmcs may fail, add a check here and move launch_state
> assignment after its success?
prepare_vmcs02() cannot fail. All the checks that need to be done on vmcs12
are done before calling it, in nested_vmx_run().
Currently, there's a single case where prepare_vmcs02 "fails" when it fails
to access apic_access_addr memory. This is wrong - the check should have been
done earlier. I'll fix that, and make prepare_vmcs02() void.
--
Nadav Har'El | Tuesday, May 24 2011, 20 Iyyar 5771
[email protected] |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |It's no use crying over spilt milk -- it
http://nadav.harel.org.il |only makes it salty for the cat.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
