[PATCH 21/30] KVM: x86: hyper-v: Check access to HVCALL_NOTIFY_LONG_SPIN_WAIT hypercall

[Vitaly Kuznetsov]

TLFS6.0b states that partition issuing HVCALL_NOTIFY_LONG_SPIN_WAIT must
posess 'UseHypercallForLongSpinWait' privilege but there's no
corresponding feature bit. Instead, we have "Recommended number of attempts
to retry a spinlock failure before notifying the hypervisor about the
failures. 0xFFFFFFFF indicates never notify." Use this to check access to
the hypercall. Also, check against zero as the corresponding CPUID must
be set (and '0' attempts before re-try is weird anyway).

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/kvm/hyperv.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 4f0ab0c50c44..bd424f2d4294 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2024,6 +2024,17 @@ static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, bool fast, u64 param)
 
 static bool hv_check_hypercall_access(struct kvm_vcpu_hv *hv_vcpu, u16 code)
 {
+	if (!hv_vcpu->enforce_cpuid)
+		return true;
+
+	switch (code) {
+	case HVCALL_NOTIFY_LONG_SPIN_WAIT:
+		return hv_vcpu->cpuid_cache.enlightenments_ebx &&
+			hv_vcpu->cpuid_cache.enlightenments_ebx != U32_MAX;
+	default:
+		break;
+	}
+
 	return true;
 }
 
-- 
2.30.2