On Mon, Feb 08, 2021, Paolo Bonzini wrote: > On 07/02/21 16:42, Jing Liu wrote: > > |In KVM, "guest_fpu" serves for any guest task working on this vcpu > > during vmexit and vmenter. We provide a pre-allocated guest_fpu space > > and entire "guest_fpu.state_mask" to avoid each dynamic features > > detection on each vcpu task. Meanwhile, to ensure correctly > > xsaves/xrstors guest state, set IA32_XFD as zero during vmexit and > > vmenter.| > > Most guests will not need the whole xstate feature set. So perhaps you > could set XFD to the host value | the guest value, trap #NM if the host XFD > is zero, and possibly reflect the exception to the guest's XFD and XFD_ERR. > > In addition, loading the guest XFD MSRs should use the MSR autoload feature > (add_atomic_switch_msr). Why do you say that? I would strongly prefer to use the load lists only if they are absolutely necessary. I don't think that's the case here, as I can't imagine accessing FPU state in NMI context is allowed, at least not without a big pile of save/restore code.
