KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division

Snapshot kvm->stats.nx_lpage_splits into a local unsigned long to avoid
64-bit division on 32-bit kernels.  Casting to an unsigned long is safe
because the maximum number of shadow pages, n_max_mmu_pages, is also an
unsigned long, i.e. KVM will start recycling shadow pages before the
number of splits can exceed a 32-bit value.

  ERROR: modpost: "__udivdi3" [arch/x86/kvm/kvm.ko] undefined!

Fixes: 7ee093d4f3f5 ("KVM: switch per-VM stats to u64")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210615162905.2132937-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -6043,6 +6043,7 @@ static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel
 
 static void kvm_recover_nx_lpages(struct kvm *kvm)
 {
+	unsigned long nx_lpage_splits = kvm->stat.nx_lpage_splits;
 	int rcu_idx;
 	struct kvm_mmu_page *sp;
 	unsigned int ratio;
@@ -6054,7 +6055,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm)
 	write_lock(&kvm->mmu_lock);
 
 	ratio = READ_ONCE(nx_huge_pages_recovery_ratio);
-	to_zap = ratio ? DIV_ROUND_UP(kvm->stat.nx_lpage_splits, ratio) : 0;
+	to_zap = ratio ? DIV_ROUND_UP(nx_lpage_splits, ratio) : 0;
 	for ( ; to_zap; --to_zap) {
 		if (list_empty(&kvm->arch.lpage_disallowed_mmu_pages))
 			break;