Re: [PATCH v2 3/7] s390/cio: Split pfn_array_alloc_pin into pieces

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On 05/14/2019 07:42 PM, Eric Farman 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 | 64 ++++++++++++++++++++++++----------
  1 file changed, 46 insertions(+), 18 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 41f48b8790bc..60aa784717c5 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 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;
  }
@@ -121,7 +132,9 @@ 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)
  {
-	vfio_unpin_pages(mdev, pa->pa_iova_pfn, pa->pa_nr);
+	/* 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);
  }
@@ -209,10 +222,16 @@ 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++) {
  		from = pa.pa_pfn[i] << PAGE_SHIFT;
@@ -559,7 +578,11 @@ 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;
@@ -589,6 +612,7 @@ 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;
@@ -627,9 +651,13 @@ 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;
  	}

Reviewed-by: Farhan Ali <alifm@xxxxxxxxxxxxx>





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