>>> On 06.12.16 at 17:23, <boris.ostrov...@oracle.com> wrote: > On 12/06/2016 06:44 AM, Jan Beulich wrote: >> --- a/xen/arch/x86/cpuid.c >> +++ b/xen/arch/x86/cpuid.c >> @@ -154,6 +154,13 @@ static void __init calculate_hvm_feature >> __set_bit(X86_FEATURE_APIC, hvm_featureset); >> >> /* >> + * Xen can often provide UMIP emulation to HVM guests even if the host >> + * doesn't have such functionality. >> + */ >> + if ( cpu_has_vmx_dt_exiting || cpu_has_svm ) >> + __set_bit(X86_FEATURE_UMIP, hvm_featureset); > > I don't think I understand how this is going to work for processors that > don't support UMIP. > > How, for example, can guest_cr[4] have X86_CR4_UMIP set on these > processors when CPUID will not show the feature being there?
What we allow the guest to see and what we store into hardware registers are two different things: Note how svm_update_guest_cr() masks off X86_CR4_UMIP from the vale to be put into the VMCB. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
