On Tue, 7 Jul 2020 at 16:15, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > Aren't you supposed to be on vacation? :-) A long vacation, enjoy! > > On Tue, Jul 07, 2020 at 10:04:22AM +0200, Paolo Bonzini wrote: > > On 07/07/20 08:11, Sean Christopherson wrote: > > > One oddity with this whole thing is that by passing through the MSR, KVM is > > > allowing the guest to write bits it doesn't know about, which is definitely > > > not normal. It also means the guest could write bits that the host VMM > > > can't. > > > > That's true. However, the main purpose of the kvm_spec_ctrl_valid_bits > > check is to ensure that host-initiated writes are valid; this way, you > > don't get a #GP on the next vmentry's WRMSR to MSR_IA32_SPEC_CTRL. > > Checking the guest CPUID bit is not even necessary. > > Right, what I'm saying is that rather than try and decipher specs to > determine what bits are supported, just throw the value at hardware and > go from there. That's effectively what we end up doing for the guest writes > anyways. > > Actually, the current behavior will break migration if there are ever legal > bits that KVM doesn't recognize, e.g. guest writes a value that KVM doesn't > allow and then migration fails when the destination tries to stuff the value > into KVM.
