[Bug 221841] KVM: nested VMX eVMCS VMPTRLD/VMPTRST causes infinite VM-Exit loop due to missing RIP advance

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=221841

--- Comment #4 from vkuznets@redhat.com ---
(In reply to vkuznets from comment #2)

> Ideally, we can try and see what genuine Hyper-V gives us
> in this situation (by e.g. running an instrumented version of KVM there). It
> does not seem that we have an extreme urgency here so I can put it to my
> backlog and try to get to it some time next week -- unless someone beats me
> to it of course!

Tested on Azure. Apparently, VMPTRLD is completely unsupported and generates
#UD right away, no matter if I give it the same 'enlightened' address or
something else. VMPTRST, however, is different: before VMLAUNCH it gives us
0xffffffffffffffff even after we set a valid eVMCS pointer to the VP assist
page. This is (AFAIU) somewhat similar to the architectural behavior when we
execute VMPTRST with no current-VMCS pointer. After VMLAUNCH it works normally
and gives us the eVMCS pointer we used. I think it makes sense to mimic the
behavior in KVM.

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