Messages in this thread | | | Date | Wed, 18 Mar 2015 11:27:01 +0100 | From | Paolo Bonzini <> | Subject | Re: regression: nested: L1 3.15+ fails to load kvm-intel on L0 <3.15 |
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On 18/03/2015 10:59, Stefan Bader wrote: >> @@ -2850,7 +2851,7 @@ static __init int setup_vmcs_config(struct >> vmcs_config *vmcs_conf) vmx_capability.ept, >> vmx_capability.vpid); } >> >> - min = 0; + min = VM_EXIT_SAVE_DEBUG_CONTROLS; #ifdef >> CONFIG_X86_64 min |= VM_EXIT_HOST_ADDR_SPACE_SIZE; #endif >> >> but I don't think it's a good idea to add it to stable kernels. > > Why is that? Because it has a risk of causing the module failing to > load on L0 where it did work before?
Because if we wanted to make 3.14 nested VMX stable-ish we would need several more, at least these:
KVM: nVMX: fix lifetime issues for vmcs02 KVM: nVMX: clean up nested_release_vmcs12 and code around it KVM: nVMX: Rework interception of IRQs and NMIs KVM: nVMX: Do not inject NMI vmexits when L2 has a pending interrupt KVM: nVMX: Disable preemption while reading from shadow VMCS
and for 3.13:
KVM: nVMX: Leave VMX mode on clearing of feature control MSR
There are also several L2-crash-L1 bugs too in Nadav Amit's patches.
Basically, nested VMX was never considered stable-worthy. Perhaps that can change soon---but not retroactively.
So I'd rather avoid giving false impressions of the stability of nVMX in 3.14.
Even if we considered nVMX stable, I'd _really_ not want to consider the L1<->L2 boundary a secure one for a longer time.
> Which would be something I would rather avoid. Generally I think it > would be good to have something that can be generally applied. > Given the speed that cloud service providers tend to move forward > (ok they may not actively push the ability to go nested).
And if they did, I'd really not want them to do it with a 3.14 kernel.
Paolo
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