s390/cio: Split pfn_array_alloc_pin into pieces

The pfn_array_alloc_pin routine is doing too much.  Today, it does the
alloc of the pfn_array struct and its member arrays, builds the iova
address lists out of a contiguous piece of guest memory, and asks vfio
to pin the resulting pages.

Let's effectively revert a significant portion of commit 5c1cfb1c
("vfio: ccw: refactor and improve pfn_array_alloc_pin()") such that we
break pfn_array_alloc_pin() into its component pieces, and have one
routine that allocates/populates the pfn_array structs, and another
that actually pins the memory.  In the future, we will be able to
handle scenarios where pinning memory isn't actually appropriate.
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Message-Id: <20190514234248.36203-4-farman@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

drivers/s390/cio/vfio_ccw_cp.c

@@ -50,28 +50,25 @@ struct ccwchain {
 };
 
 /*
- * pfn_array_alloc_pin() - alloc memory for PFNs, then pin user pages in memory
+ * pfn_array_alloc() - alloc memory for PFNs
  * @pa: pfn_array on which to perform the operation
- * @mdev: the mediated device to perform pin/unpin operations
  * @iova: target guest physical address
  * @len: number of bytes that should be pinned from @iova
  *
- * Attempt to allocate memory for PFNs, and pin user pages in memory.
+ * Attempt to allocate memory for PFNs.
  *
  * Usage of pfn_array:
  * We expect (pa_nr == 0) and (pa_iova_pfn == NULL), any field in
  * this structure will be filled in by this function.
  *
  * Returns:
- *   Number of pages pinned on success.
- *   If @pa->pa_nr is not 0, or @pa->pa_iova_pfn is not NULL initially,
- *   returns -EINVAL.
- *   If no pages were pinned, returns -errno.
+ *         0 if PFNs are allocated
+ *   -EINVAL if pa->pa_nr is not initially zero, or pa->pa_iova_pfn is not NULL
+ *   -ENOMEM if alloc failed
  */
-static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
-			       u64 iova, unsigned int len)
+static int pfn_array_alloc(struct pfn_array *pa, u64 iova, unsigned int len)
 {
-	int i, ret = 0;
+	int i;
 
 	if (!len)
 		return 0;
@@ -97,6 +94,22 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
 	for (i = 1; i < pa->pa_nr; i++)
 		pa->pa_iova_pfn[i] = pa->pa_iova_pfn[i - 1] + 1;
 
+	return 0;
+}
+
+/*
+ * pfn_array_pin() - Pin user pages in memory
+ * @pa: pfn_array on which to perform the operation
+ * @mdev: the mediated device to perform pin operations
+ *
+ * Returns number of pages pinned upon success.
+ * If the pin request partially succeeds, or fails completely,
+ * all pages are left unpinned and a negative error value is returned.
+ */
+static int pfn_array_pin(struct pfn_array *pa, struct device *mdev)
+{
+	int ret = 0;
+
 	ret = vfio_pin_pages(mdev, pa->pa_iova_pfn, pa->pa_nr,
 			     IOMMU_READ | IOMMU_WRITE, pa->pa_pfn);
 
@@ -112,8 +125,6 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
 
 err_out:
 	pa->pa_nr = 0;
-	kfree(pa->pa_iova_pfn);
-	pa->pa_iova_pfn = NULL;
 
 	return ret;
 }
@@ -121,6 +132,8 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
 /* Unpin the pages before releasing the memory. */
 static void pfn_array_unpin_free(struct pfn_array *pa, struct device *mdev)
 {
+	/* Only unpin if any pages were pinned to begin with */
+	if (pa->pa_nr)
 		vfio_unpin_pages(mdev, pa->pa_iova_pfn, pa->pa_nr);
 	pa->pa_nr = 0;
 	kfree(pa->pa_iova_pfn);
@@ -209,9 +222,15 @@ static long copy_from_iova(struct device *mdev,
 	int i, ret;
 	unsigned long l, m;
 
-	ret = pfn_array_alloc_pin(&pa, mdev, iova, n);
-	if (ret <= 0)
+	ret = pfn_array_alloc(&pa, iova, n);
+	if (ret < 0)
+		return ret;
+
+	ret = pfn_array_pin(&pa, mdev);
+	if (ret < 0) {
+		pfn_array_unpin_free(&pa, mdev);
 		return ret;
+	}
 
 	l = n;
 	for (i = 0; i < pa.pa_nr; i++) {
@@ -560,7 +579,11 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
 	if (ret)
 		goto out_init;
 
-	ret = pfn_array_alloc_pin(pat->pat_pa, cp->mdev, ccw->cda, ccw->count);
+	ret = pfn_array_alloc(pat->pat_pa, ccw->cda, ccw->count);
+	if (ret < 0)
+		goto out_unpin;
+
+	ret = pfn_array_pin(pat->pat_pa, cp->mdev);
 	if (ret < 0)
 		goto out_unpin;
 
@@ -590,6 +613,7 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
 {
 	struct ccw1 *ccw;
 	struct pfn_array_table *pat;
+	struct pfn_array *pa;
 	unsigned long *idaws;
 	u64 idaw_iova;
 	unsigned int idaw_nr, idaw_len;
@@ -628,9 +652,13 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
 
 	for (i = 0; i < idaw_nr; i++) {
 		idaw_iova = *(idaws + i);
+		pa = pat->pat_pa + i;
+
+		ret = pfn_array_alloc(pa, idaw_iova, 1);
+		if (ret < 0)
+			goto out_free_idaws;
 
-		ret = pfn_array_alloc_pin(pat->pat_pa + i, cp->mdev,
-					  idaw_iova, 1);
+		ret = pfn_array_pin(pa, cp->mdev);
 		if (ret < 0)
 			goto out_free_idaws;
 	}