KVM: reorganize hva_to_pfn

We do too many things in hva_to_pfn, this patch reorganize the code,
let it be better readable
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/kvm_main.c

@@ -1041,25 +1041,41 @@ static inline int check_user_page_hwpoison(unsigned long addr)
 	return rc == -EHWPOISON;
 }
 
-static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
-			bool write_fault, bool *writable)
+/*
+ * The atomic path to get the writable pfn which will be stored in @pfn,
+ * true indicates success, otherwise false is returned.
+ */
+static bool hva_to_pfn_fast(unsigned long addr, bool atomic, bool *async,
+			    bool write_fault, bool *writable, pfn_t *pfn)
 {
 	struct page *page[1];
-	int npages = 0;
-	pfn_t pfn;
+	int npages;
 
-	/* we can do it either atomically or asynchronously, not both */
-	BUG_ON(atomic && async);
+	if (!(async || atomic))
+		return false;
 
-	BUG_ON(!write_fault && !writable);
+	npages = __get_user_pages_fast(addr, 1, 1, page);
+	if (npages == 1) {
+		*pfn = page_to_pfn(page[0]);
 
 		if (writable)
 			*writable = true;
+		return true;
+	}
 
-	if (atomic || async)
-		npages = __get_user_pages_fast(addr, 1, 1, page);
+	return false;
+}
+
+/*
+ * The slow path to get the pfn of the specified host virtual address,
+ * 1 indicates success, -errno is returned if error is detected.
+ */
+static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
+			   bool *writable, pfn_t *pfn)
+{
+	struct page *page[1];
+	int npages = 0;
 
-	if (unlikely(npages != 1) && !atomic) {
 	might_sleep();
 
 	if (writable)
@@ -1073,9 +1089,11 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
 	} else
 		npages = get_user_pages_fast(addr, 1, write_fault,
 					     page);
+	if (npages != 1)
+		return npages;
 
 	/* map read fault as writable if possible */
-		if (unlikely(!write_fault) && npages == 1) {
+	if (unlikely(!write_fault)) {
 		struct page *wpage[1];
 
 		npages = __get_user_pages_fast(addr, 1, 1, wpage);
@@ -1084,24 +1102,43 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
 			put_page(page[0]);
 			page[0] = wpage[0];
 		}
+
 		npages = 1;
 	}
-	}
+	*pfn = page_to_pfn(page[0]);
+	return npages;
+}
 
-	if (unlikely(npages != 1)) {
+static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
+			bool write_fault, bool *writable)
+{
 	struct vm_area_struct *vma;
+	pfn_t pfn = 0;
+	int npages;
+
+	/* we can do it either atomically or asynchronously, not both */
+	BUG_ON(atomic && async);
+
+	BUG_ON(!write_fault && !writable);
+
+	if (hva_to_pfn_fast(addr, atomic, async, write_fault, writable, &pfn))
+		return pfn;
 
 	if (atomic)
 		return KVM_PFN_ERR_FAULT;
 
+	npages = hva_to_pfn_slow(addr, async, write_fault, writable, &pfn);
+	if (npages == 1)
+		return pfn;
+
 	down_read(&current->mm->mmap_sem);
 	if (npages == -EHWPOISON ||
 	      (!async && check_user_page_hwpoison(addr))) {
-			up_read(&current->mm->mmap_sem);
-			return KVM_PFN_ERR_HWPOISON;
+		pfn = KVM_PFN_ERR_HWPOISON;
+		goto exit;
 	}
 
-		vma = find_vma_intersection(current->mm, addr, addr+1);
+	vma = find_vma_intersection(current->mm, addr, addr + 1);
 
 	if (vma == NULL)
 		pfn = KVM_PFN_ERR_FAULT;
@@ -1114,10 +1151,8 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
 			*async = true;
 		pfn = KVM_PFN_ERR_FAULT;
 	}
+exit:
 	up_read(&current->mm->mmap_sem);
-	} else
-		pfn = page_to_pfn(page[0]);
-
 	return pfn;
 }