[PATCH v3 04/10] vfio/ccw: Only pass in contiguous pages

Nicolin Chen
2022-07-08T22:44:58Z

This driver is the only caller of vfio_pin/unpin_pages that might pass
in a non-contiguous PFN list, but in many cases it has a contiguous PFN
list to process. So letting VFIO API handle a non-contiguous PFN list
is actually counterproductive.

Add a pair of simple loops to pass in contiguous PFNs only, to have an
efficient implementation in VFIO.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Tested-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/s390/cio/vfio_ccw_cp.c | 70 +++++++++++++++++++++++++++-------
1 file changed, 56 insertions(+), 14 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 0c2be9421ab7..3b94863ad24e 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -90,6 +90,38 @@ static int pfn_array_alloc(struct pfn_array *pa, u64 iova, unsigned int len)
return 0;
}

+/*
+ * pfn_array_unpin() - Unpin user pages in memory
+ * @pa: pfn_array on which to perform the operation
+ * @vdev: the vfio device to perform the operation
+ * @pa_nr: number of user pages to unpin
+ *
+ * Only unpin if any pages were pinned to begin with, i.e. pa_nr > 0,
+ * otherwise only clear pa->pa_nr
+ */
+static void pfn_array_unpin(struct pfn_array *pa,
+ struct vfio_device *vdev, int pa_nr)
+{
+ int unpinned = 0, npage = 1;
+
+ while (unpinned < pa_nr) {
+ unsigned long *first = &pa->pa_iova_pfn[unpinned];
+ unsigned long *last = &first[npage];
+
+ if (unpinned + npage < pa_nr &&
+ *first + npage == *last) {
+ npage++;
+ continue;
+ }
+
+ vfio_unpin_pages(vdev, first, npage);
+ unpinned += npage;
+ npage = 1;
+ }
+
+ pa->pa_nr = 0;
+}
+
/*
* pfn_array_pin() - Pin user pages in memory
* @pa: pfn_array on which to perform the operation
@@ -101,34 +133,44 @@ static int pfn_array_alloc(struct pfn_array *pa, u64 iova, unsigned int len)
*/
static int pfn_array_pin(struct pfn_array *pa, struct vfio_device *vdev)
{
+ int pinned = 0, npage = 1;
int ret = 0;

- ret = vfio_pin_pages(vdev, pa->pa_iova_pfn, pa->pa_nr,
- IOMMU_READ | IOMMU_WRITE, pa->pa_pfn);
+ while (pinned < pa->pa_nr) {
+ unsigned long *first = &pa->pa_iova_pfn[pinned];
+ unsigned long *last = &first[npage];

- if (ret < 0) {
- goto err_out;
- } else if (ret > 0 && ret != pa->pa_nr) {
- vfio_unpin_pages(vdev, pa->pa_iova_pfn, ret);
- ret = -EINVAL;
- goto err_out;
+ if (pinned + npage < pa->pa_nr &&
+ *first + npage == *last) {
+ npage++;
+ continue;
+ }
+
+ ret = vfio_pin_pages(vdev, first, npage,
+ IOMMU_READ | IOMMU_WRITE,
+ &pa->pa_pfn[pinned]);
+ if (ret < 0) {
+ goto err_out;
+ } else if (ret > 0 && ret != npage) {
+ pinned += ret;
+ ret = -EINVAL;
+ goto err_out;
+ }
+ pinned += npage;
+ npage = 1;
}

return ret;

err_out:
- pa->pa_nr = 0;
-
+ pfn_array_unpin(pa, vdev, pinned);
return ret;
}

/* Unpin the pages before releasing the memory. */
static void pfn_array_unpin_free(struct pfn_array *pa, struct vfio_device *vdev)
{
- /* Only unpin if any pages were pinned to begin with */
- if (pa->pa_nr)
- vfio_unpin_pages(vdev, pa->pa_iova_pfn, pa->pa_nr);
- pa->pa_nr = 0;
+ pfn_array_unpin(pa, vdev, pa->pa_nr);
kfree(pa->pa_iova_pfn);
}

--
2.17.1