KVM: x86: hyperv: declare KVM_CAP_HYPERV_TLBFLUSH capability

We need a new capability to indicate support for the newly added
HvFlushVirtualAddress{List,Space}{,Ex} hypercalls. Upon seeing this
capability, userspace is supposed to announce PV TLB flush features
by setting the appropriate CPUID bits (if needed).
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

Documentation/virtual/kvm/api.txt

@@ -4603,3 +4603,12 @@ Architectures: s390
 This capability indicates that kvm will implement the interfaces to handle
 reset, migration and nested KVM for branch prediction blocking. The stfle
 facility 82 should not be provided to the guest without this capability.
+
+8.14 KVM_CAP_HYPERV_TLBFLUSH
+
+Architectures: x86
+
+This capability indicates that KVM supports paravirtualized Hyper-V TLB Flush
+hypercalls:
+HvFlushVirtualAddressSpace, HvFlushVirtualAddressSpaceEx,
+HvFlushVirtualAddressList, HvFlushVirtualAddressListEx.

arch/x86/kvm/x86.c

@@ -2871,6 +2871,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_HYPERV_SYNIC2:
 	case KVM_CAP_HYPERV_VP_INDEX:
 	case KVM_CAP_HYPERV_EVENTFD:
+	case KVM_CAP_HYPERV_TLBFLUSH:
 	case KVM_CAP_PCI_SEGMENT:
 	case KVM_CAP_DEBUGREGS:
 	case KVM_CAP_X86_ROBUST_SINGLESTEP:

include/uapi/linux/kvm.h

@@ -948,6 +948,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_S390_BPB 152
 #define KVM_CAP_GET_MSR_FEATURES 153
 #define KVM_CAP_HYPERV_EVENTFD 154
+#define KVM_CAP_HYPERV_TLBFLUSH 155
 
 #ifdef KVM_CAP_IRQ_ROUTING