Messages in this thread | | | Subject | Re: [PATCH 03/28] KVM: nSVM: inject exceptions via svm_check_nested_events | From | Paolo Bonzini <> | Date | Sat, 6 Mar 2021 10:26:56 +0100 |
| |
On 06/03/21 02:39, Sean Christopherson wrote: > Unless KVM (L0) knowingly wants to override L1, e.g. KVM_GUESTDBG_* cases, KVM > shouldn't do a damn thing except forward the exception to L1 if L1 wants the > exception. > > ud_interception() and gp_interception() do quite a bit before forwarding the > exception, and in the case of #UD, it's entirely possible the #UD will never get > forwarded to L1. #GP is even more problematic because it's a contributory > exception, and kvm_multiple_exception() is not equipped to check and handle > nested intercepts before vectoring the exception, which means KVM will > incorrectly escalate a #GP->#DF and #GP->#DF->Triple Fault instead of exiting > to L1. That's a wee bit problematic since KVM also has a soon-to-be-fixed bug > where it kills L1 on a Triple Fault in L2...
I agree with the #GP problem, but this is on purpose. For example, if L1 CPUID has MOVBE and it is being emulated via #UD, L1 would be right to set MOVBE in L2's CPUID and expect it not to cause a #UD. The same is true for the VMware #GP interception case.
Maxim is also working on this, the root cause is that kvm_multiple_exception()'s escalation of contributory exceptions to #DF and triple fault is incorrect in the case of nested virtualization.
Paolo
| |