Re: [PATCH 3/7] s390/cio: Split pfn_array_alloc_pin into pieces

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On 5/8/19 6:43 AM, Cornelia Huck wrote:
On Fri,  3 May 2019 15:49:08 +0200
Eric Farman <farman@xxxxxxxxxxxxx> wrote:

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 5c1cfb1c3948
("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@xxxxxxxxxxxxx>
---
  drivers/s390/cio/vfio_ccw_cp.c | 72 +++++++++++++++++++++++++++---------------
  1 file changed, 47 insertions(+), 25 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index f86da78eaeaa..b70306c06150 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/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 PFN.

s/PFN/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;
@@ -97,23 +94,33 @@ 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 on success.
+ *   If fewer pages than requested were pinned, returns -EINVAL
+ *   If no pages were pinned, returns -errno.

I don't really like the 'returns -errno' :) It's actually the return
code of vfio_pin_pages(), and that might include -EINVAL as well.

So, what about mentioning in the function description that
pfn_array_pin() only succeeds if it coult pin all pages, and simply
stating that it returns a negative error value on failure?

Seems reasonable to me...  Something like:

 * 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);
- if (ret < 0) {
-		goto err_out;
-	} else if (ret > 0 && ret != pa->pa_nr) {
+	if (ret > 0 && ret != pa->pa_nr) {
  		vfio_unpin_pages(mdev, pa->pa_iova_pfn, ret);
  		ret = -EINVAL;
-		goto err_out;
  	}
- return ret;
-
-err_out:
-	pa->pa_nr = 0;
-	kfree(pa->pa_iova_pfn);
-	pa->pa_iova_pfn = NULL;
+	if (ret < 0)
+		pa->pa_iova = 0;
return ret;
  }

(...)




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