KVM: x86: Add a helper to get the sparse VP_SET for IPIs and TLB flushes

Add a helper, kvm_get_sparse_vp_set(), to handle sanity checks related to
the VARHEAD field and reading the sparse banks of a VP_SET.  A future
commit to reduce the memory footprint of sparse_banks will introduce more
common code to the sparse bank retrieval.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211207220926.718794-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -1754,10 +1754,19 @@ struct kvm_hv_hcall {
 	sse128_t xmm[HV_HYPERCALL_MAX_XMM_REGISTERS];
 };
 
+static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
+				 u64 *sparse_banks, gpa_t offset)
+{
+	if (hc->var_cnt > 64)
+		return -EINVAL;
+
+	return kvm_read_guest(kvm, hc->ingpa + offset, sparse_banks,
+			      hc->var_cnt * sizeof(*sparse_banks));
+}
+
 static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool ex)
 {
 	int i;
-	gpa_t gpa;
 	struct kvm *kvm = vcpu->kvm;
 	struct hv_tlb_flush_ex flush_ex;
 	struct hv_tlb_flush flush;
@@ -1834,13 +1843,9 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 			goto do_flush;
 		}
 
-		if (hc->var_cnt > 64)
-			return HV_STATUS_INVALID_HYPERCALL_INPUT;
-
-		gpa = hc->ingpa + offsetof(struct hv_tlb_flush_ex,
-					   hv_vp_set.bank_contents);
-		if (unlikely(kvm_read_guest(kvm, gpa, sparse_banks,
-					    hc->var_cnt * sizeof(sparse_banks[0]))))
+		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks,
+					  offsetof(struct hv_tlb_flush_ex,
+						   hv_vp_set.bank_contents)))
 			return HV_STATUS_INVALID_HYPERCALL_INPUT;
 	}
 
@@ -1937,14 +1942,9 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 		if (!hc->var_cnt)
 			goto ret_success;
 
-		if (hc->var_cnt > 64)
-			return HV_STATUS_INVALID_HYPERCALL_INPUT;
-
-		if (kvm_read_guest(kvm,
-				   hc->ingpa + offsetof(struct hv_send_ipi_ex,
-							vp_set.bank_contents),
-				   sparse_banks,
-				   hc->var_cnt * sizeof(sparse_banks[0])))
+		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks,
+					  offsetof(struct hv_send_ipi_ex,
+						   vp_set.bank_contents)))
 			return HV_STATUS_INVALID_HYPERCALL_INPUT;
 	}