KVM: export __gfn_to_pfn_memslot, drop gfn_to_pfn_async

gfn_to_pfn_async is used in just one place, and because of x86-specific
treatment that place will need to look at the memory slot.  Hence inline
it into try_async_pf and export __gfn_to_pfn_memslot.

The patch also switches the subsequent call to gfn_to_pfn_prot to use
__gfn_to_pfn_memslot.  This is a small optimization.  Finally, remove
the now-unused async argument of __gfn_to_pfn.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -3511,10 +3511,12 @@ static bool can_do_async_pf(struct kvm_vcpu *vcpu)
 static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
 			 gva_t gva, pfn_t *pfn, bool write, bool *writable)
 {
+	struct kvm_memory_slot *slot;
 	bool async;
 
-	*pfn = gfn_to_pfn_async(vcpu->kvm, gfn, &async, write, writable);
-
+	slot = gfn_to_memslot(vcpu->kvm, gfn);
+	async = false;
+	*pfn = __gfn_to_pfn_memslot(slot, gfn, false, &async, write, writable);
 	if (!async)
 		return false; /* *pfn has correct page already */
 
@@ -3528,8 +3530,7 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
 			return true;
 	}
 
-	*pfn = gfn_to_pfn_prot(vcpu->kvm, gfn, write, writable);
-
+	*pfn = __gfn_to_pfn_memslot(slot, gfn, false, NULL, write, writable);
 	return false;
 }