x86/hyperv: Introduce HV_MAX_SPARSE_VCPU_BANKS/HV_VCPUS_PER_SPARSE_BANK constants

It may not come clear from where the magical '64' value used in
__cpumask_to_vpset() come from. Moreover, '64' means both the maximum
sparse bank number as well as the number of vCPUs per bank. Add defines
to make things clear. These defines are also going to be used by KVM.

No functional change.
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-15-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/asm-generic/hyperv-tlfs.h

@@ -399,6 +399,11 @@ struct hv_vpset {
 	u64 bank_contents[];
 } __packed;
 
+/* The maximum number of sparse vCPU banks which can be encoded by 'struct hv_vpset' */
+#define HV_MAX_SPARSE_VCPU_BANKS (64)
+/* The number of vCPUs in one sparse bank */
+#define HV_VCPUS_PER_SPARSE_BANK (64)
+
 /* HvCallSendSyntheticClusterIpi hypercall */
 struct hv_send_ipi {
 	u32 vector;

include/asm-generic/mshyperv.h

@@ -211,9 +211,10 @@ static inline int __cpumask_to_vpset(struct hv_vpset *vpset,
 {
 	int cpu, vcpu, vcpu_bank, vcpu_offset, nr_bank = 1;
 	int this_cpu = smp_processor_id();
+	int max_vcpu_bank = hv_max_vp_index / HV_VCPUS_PER_SPARSE_BANK;
 
-	/* valid_bank_mask can represent up to 64 banks */
-	if (hv_max_vp_index / 64 >= 64)
+	/* vpset.valid_bank_mask can represent up to HV_MAX_SPARSE_VCPU_BANKS banks */
+	if (max_vcpu_bank >= HV_MAX_SPARSE_VCPU_BANKS)
 		return 0;
 
 	/*
@@ -221,7 +222,7 @@ static inline int __cpumask_to_vpset(struct hv_vpset *vpset,
 	 * structs are not cleared between calls, we risk flushing unneeded
 	 * vCPUs otherwise.
 	 */
-	for (vcpu_bank = 0; vcpu_bank <= hv_max_vp_index / 64; vcpu_bank++)
+	for (vcpu_bank = 0; vcpu_bank <= max_vcpu_bank; vcpu_bank++)
 		vpset->bank_contents[vcpu_bank] = 0;
 
 	/*
@@ -233,8 +234,8 @@ static inline int __cpumask_to_vpset(struct hv_vpset *vpset,
 		vcpu = hv_cpu_number_to_vp_number(cpu);
 		if (vcpu == VP_INVAL)
 			return -1;
-		vcpu_bank = vcpu / 64;
-		vcpu_offset = vcpu % 64;
+		vcpu_bank = vcpu / HV_VCPUS_PER_SPARSE_BANK;
+		vcpu_offset = vcpu % HV_VCPUS_PER_SPARSE_BANK;
 		__set_bit(vcpu_offset, (unsigned long *)
 			  &vpset->bank_contents[vcpu_bank]);
 		if (vcpu_bank >= nr_bank)