Re: [PATCH v4 2/2] KVM: nSVM: implement ondemand allocation of the nested state

From: Paolo Bonzini
Date: Sun Sep 20 2020 - 12:42:49 EST

On 20/09/20 18:16, Sean Christopherson wrote:
>> Maxim, your previous version was adding some error handling to
>> kvm_x86_ops.set_efer. I don't remember what was the issue; did you have
>> any problems propagating all the errors up to KVM_SET_SREGS (easy),
>> kvm_set_msr (harder) etc.?
> I objected to letting .set_efer() return a fault.

So did I, and that's why we get KVM_REQ_OUT_OF_MEMORY. But it was more
of an "it's ugly and it ought not to fail" thing than something I could

It looks like we agree, but still we have to choose the lesser evil?


> A relatively minor issue is
> the code in vmx_set_efer() that handles lack of EFER because technically KVM
> can emulate EFER.SCE+SYSCALL without supporting EFER in hardware. Returning
> success/'0' would avoid that particular issue. My primary concern is that I'd
> prefer not to add another case where KVM can potentially ignore a fault
> indicated by a helper, a la vmx_set_cr4().