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Presence of the "virtual interrupt delivery" feature will > > > > be reported using a different option. > > > > > > > > Signed-off-by: Roger Pau Monné > > > > --- > > > > I find the logic in vmx_vlapic_msr_changed() hard to follow, but I > > > > don't want to rewrite the function logic at this point. > > > > --- > > > > xen/arch/x86/hvm/viridian/viridian.c | 2 +- > > > > xen/arch/x86/hvm/vmx/vmcs.c | 8 ++++---- > > > > xen/arch/x86/hvm/vmx/vmx.c | 25 ++++++++++++++++++------- > > > > xen/arch/x86/traps.c | 4 +--- > > > > 4 files changed, 24 insertions(+), 15 deletions(-) > > > > > > > > diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c > > > > index c4fa0a8b32..bafd8e90de 100644 > > > > --- a/xen/arch/x86/hvm/viridian/viridian.c > > > > +++ b/xen/arch/x86/hvm/viridian/viridian.c > > > > @@ -201,7 +201,7 @@ void cpuid_viridian_leaves(const struct vcpu *v, uint32_t leaf, > > > > * Suggest x2APIC mode by default, unless xAPIC registers are hardware > > > > * virtualized and x2APIC ones aren't. > > > > */ > > > > - if ( !cpu_has_vmx_apic_reg_virt || cpu_has_vmx_virtualize_x2apic_mode ) > > > > + if ( !has_assisted_xapic(d) || has_assisted_x2apic(d) ) > > > > > > So, not sure why this is separated from patch 1 but stated this way it seems > > > counterintuitive. We only want to use the viridian MSRs if they are going to > > > be more efficient.. which I think is only in the case where we have neither > > > an x2apic not an assisted xapic (hence we would trap for MMIO). > > > > I've read the MS HTLFS and I guess I got confused, the section about > > this CPUID bit states: > > > > "Bit 3: Recommend using MSRs for accessing APIC registers EOI, ICR and > > TPR rather than their memory-mapped" > > > > So I've (wrongly) understood that MSRs for accessing APIC registers > > was meant to be a recommendation to use x2APIC mode in order to access > > those registers. Didn't realize Viridian had a way to expose certain > > APIC registers using MSRs when the APIC is in xAPIC mode. > > > > Yeah, I think they predate the existence of x2apic. > > > I withdraw patch 1 and adjust patch 2 accordingly then. > > > Cool. Thanks, How does Windows know whether to use xAPIC or x2APIC? I would assume CPUID4A_MSR_BASED_APIC only makes sense when in xAPIC mode, as otherwise the registers are already accesses using MSRs. Thanks, Roger.