[PATCH RFC untested] kvm/x86: implement hv EOI assist

["Michael S. Tsirkin" <mst@redhat.com>]

It seems that it's easy to implement the EOI assist
on top of the PV EOI feature: simply convert the
page address to the format expected by PV EOI.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---

Warning: untested! As I'll be off-line for a couple of days,
sending this out for early review.
Review/comments/flames/testing reports welcome.

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8ae1ff5..d84d750fc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1890,6 +1890,8 @@ static int set_msr_hyperv(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 
 		if (!(data & HV_X64_MSR_APIC_ASSIST_PAGE_ENABLE)) {
 			vcpu->arch.hv_vapic = data;
+			if (kvm_lapic_enable_pv_eoi(vcpu, 0))
+				return 1;
 			break;
 		}
 		gfn = data >> HV_X64_MSR_APIC_ASSIST_PAGE_ADDRESS_SHIFT;
@@ -1900,6 +1902,8 @@ static int set_msr_hyperv(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 			return 1;
 		vcpu->arch.hv_vapic = data;
 		mark_page_dirty(vcpu->kvm, gfn);
+		if (kvm_lapic_enable_pv_eoi(vcpu, gfn_to_gpa(gfn) | KVM_MSR_ENABLED))
+			return 1;
 		break;
 	}
 	case HV_X64_MSR_EOI: