[PATCH v2 05/16] vfio/ccw: replace copy_from_iova with vfio_dma_rw

Eric Farman
2022-12-20T17:10:50Z

It was suggested [1] that we replace the old copy_from_iova() routine
(which pins a page, does a memcpy, and unpins the page) with the
newer vfio_dma_rw() interface.

This has a modest improvement in the overall time spent through the
fsm_io_request() path, and simplifies some of the code to boot.

[1] https://lore.kernel.org/r/20220706170553.GK693670@nvidia.com/

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
drivers/s390/cio/vfio_ccw_cp.c | 56 +++-------------------------------
1 file changed, 5 insertions(+), 51 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 3a11132b1685..1eacbb8dc860 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -228,51 +228,6 @@ static void convert_ccw0_to_ccw1(struct ccw1 *source, unsigned long len)
}
}

-/*
- * Within the domain (@vdev), copy @n bytes from a guest physical
- * address (@iova) to a host physical address (@to).
- */
-static long copy_from_iova(struct vfio_device *vdev, void *to, u64 iova,
- unsigned long n)
-{
- struct page_array pa = {0};
- int i, ret;
- unsigned long l, m;
-
- ret = page_array_alloc(&pa, iova, n);
- if (ret < 0)
- return ret;
-
- ret = page_array_pin(&pa, vdev);
- if (ret < 0) {
- page_array_unpin_free(&pa, vdev);
- return ret;
- }
-
- l = n;
- for (i = 0; i < pa.pa_nr; i++) {
- void *from = kmap_local_page(pa.pa_page[i]);
-
- m = PAGE_SIZE;
- if (i == 0) {
- from += iova & (PAGE_SIZE - 1);
- m -= iova & (PAGE_SIZE - 1);
- }
-
- m = min(l, m);
- memcpy(to + (n - l), from, m);
- kunmap_local(from);
-
- l -= m;
- if (l == 0)
- break;
- }
-
- page_array_unpin_free(&pa, vdev);
-
- return l;
-}
-
/*
* Helpers to operate ccwchain.
*/
@@ -471,10 +426,9 @@ static int ccwchain_handle_ccw(u32 cda, struct channel_program *cp)
int len, ret;

/* Copy 2K (the most we support today) of possible CCWs */
- len = copy_from_iova(vdev, cp->guest_cp, cda,
- CCWCHAIN_LEN_MAX * sizeof(struct ccw1));
- if (len)
- return len;
+ ret = vfio_dma_rw(vdev, cda, cp->guest_cp, CCWCHAIN_LEN_MAX * sizeof(struct ccw1), false);
+ if (ret)
+ return ret;

/* Convert any Format-0 CCWs to Format-1 */
if (!cp->orb.cmd.fmt)
@@ -572,7 +526,7 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
if (ccw_is_idal(ccw)) {
/* Read first IDAW to see if it's 4K-aligned or not. */
/* All subsequent IDAws will be 4K-aligned. */
- ret = copy_from_iova(vdev, &iova, ccw->cda, sizeof(iova));
+ ret = vfio_dma_rw(vdev, ccw->cda, &iova, sizeof(iova), false);
if (ret)
return ret;
} else {
@@ -601,7 +555,7 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,

if (ccw_is_idal(ccw)) {
/* Copy guest IDAL into host IDAL */
- ret = copy_from_iova(vdev, idaws, ccw->cda, idal_len);
+ ret = vfio_dma_rw(vdev, ccw->cda, idaws, idal_len, false);
if (ret)
goto out_unpin;

--
2.34.1