KVM: x86: hyper-v: Use HV_MAX_SPARSE_VCPU_BANKS/HV_VCPUS_PER_SPARSE_BANK instead of raw '64'

It may not be clear from where the '64' limit for the maximum sparse
bank number comes from, use HV_MAX_SPARSE_VCPU_BANKS define instead.
Use HV_VCPUS_PER_SPARSE_BANK in KVM_HV_MAX_SPARSE_VCPU_SET_BITS's
definition. Opportunistically adjust the comment around BUILD_BUG_ON().

No functional change.
Suggested-by: Sean Christopherson <seanjc@google.com>
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: <20221101145426.251680-16-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -40,7 +40,7 @@
 #include "irq.h"
 #include "fpu.h"
 
-#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64)
+#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, HV_VCPUS_PER_SPARSE_BANK)
 
 static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,
 				bool vcpu_kick);
@@ -1793,7 +1793,7 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
 				 u64 *sparse_banks, int consumed_xmm_halves,
 				 gpa_t offset)
 {
-	if (hc->var_cnt > 64)
+	if (hc->var_cnt > HV_MAX_SPARSE_VCPU_BANKS)
 		return -EINVAL;
 
 	/* Cap var_cnt to ignore banks that cannot contain a legal VP index. */
@@ -1902,12 +1902,11 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 	gpa_t data_offset;
 
 	/*
-	 * The Hyper-V TLFS doesn't allow more than 64 sparse banks, e.g. the
-	 * valid mask is a u64.  Fail the build if KVM's max allowed number of
-	 * vCPUs (>4096) would exceed this limit, KVM will additional changes
-	 * for Hyper-V support to avoid setting the guest up to fail.
+	 * The Hyper-V TLFS doesn't allow more than HV_MAX_SPARSE_VCPU_BANKS
+	 * sparse banks. Fail the build if KVM's max allowed number of
+	 * vCPUs (>4096) exceeds this limit.
 	 */
-	BUILD_BUG_ON(KVM_HV_MAX_SPARSE_VCPU_SET_BITS > 64);
+	BUILD_BUG_ON(KVM_HV_MAX_SPARSE_VCPU_SET_BITS > HV_MAX_SPARSE_VCPU_BANKS);
 
 	/*
 	 * 'Slow' hypercall's first parameter is the address in guest's memory