qdisk - hw/block/xen_disk: grant copy implementation

Copy data operated on during request from/to local buffers to/from
the grant references.

Before grant copy operation local buffers must be allocated what is
done by calling ioreq_init_copy_buffers. For the 'read' operation,
first, the qemu device invokes the read operation on local buffers
and on the completion grant copy is called and buffers are freed.
For the 'write' operation grant copy is performed before invoking
write by qemu device.

A new value 'feature_grant_copy' is added to recognize when the
grant copy operation is supported by a guest.

Signed-off-by: Paulina Szubarczyk <paulinaszubarczyk@gmail.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

1 files changed, 148 insertions, 5 deletions

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 342868904d..5aa350a1bf 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -119,6 +119,9 @@ struct XenBlkDev {
     unsigned int        persistent_gnt_count;
     unsigned int        max_grants;
 
+    /* Grant copy */
+    gboolean            feature_grant_copy;
+
     /* qemu block driver */
     DriveInfo           *dinfo;
     BlockBackend        *blk;
@@ -489,6 +492,106 @@ static int ioreq_map(struct ioreq *ioreq)
     return 0;
 }
 
+#if CONFIG_XEN_CTRL_INTERFACE_VERSION >= 480
+
+static void ioreq_free_copy_buffers(struct ioreq *ioreq)
+{
+    int i;
+
+    for (i = 0; i < ioreq->v.niov; i++) {
+        ioreq->page[i] = NULL;
+    }
+
+    qemu_vfree(ioreq->pages);
+}
+
+static int ioreq_init_copy_buffers(struct ioreq *ioreq)
+{
+    int i;
+
+    if (ioreq->v.niov == 0) {
+        return 0;
+    }
+
+    ioreq->pages = qemu_memalign(XC_PAGE_SIZE, ioreq->v.niov * XC_PAGE_SIZE);
+
+    for (i = 0; i < ioreq->v.niov; i++) {
+        ioreq->page[i] = ioreq->pages + i * XC_PAGE_SIZE;
+        ioreq->v.iov[i].iov_base = ioreq->page[i];
+    }
+
+    return 0;
+}
+
+static int ioreq_grant_copy(struct ioreq *ioreq)
+{
+    xengnttab_handle *gnt = ioreq->blkdev->xendev.gnttabdev;
+    xengnttab_grant_copy_segment_t segs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+    int i, count, rc;
+    int64_t file_blk = ioreq->blkdev->file_blk;
+
+    if (ioreq->v.niov == 0) {
+        return 0;
+    }
+
+    count = ioreq->v.niov;
+
+    for (i = 0; i < count; i++) {
+        if (ioreq->req.operation == BLKIF_OP_READ) {
+            segs[i].flags = GNTCOPY_dest_gref;
+            segs[i].dest.foreign.ref = ioreq->refs[i];
+            segs[i].dest.foreign.domid = ioreq->domids[i];
+            segs[i].dest.foreign.offset = ioreq->req.seg[i].first_sect * file_blk;
+            segs[i].source.virt = ioreq->v.iov[i].iov_base;
+        } else {
+            segs[i].flags = GNTCOPY_source_gref;
+            segs[i].source.foreign.ref = ioreq->refs[i];
+            segs[i].source.foreign.domid = ioreq->domids[i];
+            segs[i].source.foreign.offset = ioreq->req.seg[i].first_sect * file_blk;
+            segs[i].dest.virt = ioreq->v.iov[i].iov_base;
+        }
+        segs[i].len = (ioreq->req.seg[i].last_sect
+                       - ioreq->req.seg[i].first_sect + 1) * file_blk;
+    }
+
+    rc = xengnttab_grant_copy(gnt, count, segs);
+
+    if (rc) {
+        xen_be_printf(&ioreq->blkdev->xendev, 0,
+                      "failed to copy data %d\n", rc);
+        ioreq->aio_errors++;
+        return -1;
+    }
+
+    for (i = 0; i < count; i++) {
+        if (segs[i].status != GNTST_okay) {
+            xen_be_printf(&ioreq->blkdev->xendev, 3,
+                          "failed to copy data %d for gref %d, domid %d\n",
+                          segs[i].status, ioreq->refs[i], ioreq->domids[i]);
+            ioreq->aio_errors++;
+            rc = -1;
+        }
+    }
+
+    return rc;
+}
+#else
+static void ioreq_free_copy_buffers(struct ioreq *ioreq)
+{
+    abort();
+}
+
+static int ioreq_init_copy_buffers(struct ioreq *ioreq)
+{
+    abort();
+}
+
+static int ioreq_grant_copy(struct ioreq *ioreq)
+{
+    abort();
+}
+#endif
+
 static int ioreq_runio_qemu_aio(struct ioreq *ioreq);
 
 static void qemu_aio_complete(void *opaque, int ret)
@@ -511,8 +614,31 @@ static void qemu_aio_complete(void *opaque, int ret)
         return;
     }
 
+    if (ioreq->blkdev->feature_grant_copy) {
+        switch (ioreq->req.operation) {
+        case BLKIF_OP_READ:
+            /* in case of failure ioreq->aio_errors is increased */
+            if (ret == 0) {
+                ioreq_grant_copy(ioreq);
+            }
+            ioreq_free_copy_buffers(ioreq);
+            break;
+        case BLKIF_OP_WRITE:
+        case BLKIF_OP_FLUSH_DISKCACHE:
+            if (!ioreq->req.nr_segments) {
+                break;
+            }
+            ioreq_free_copy_buffers(ioreq);
+            break;
+        default:
+            break;
+        }
+    }
+
     ioreq->status = ioreq->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
-    ioreq_unmap(ioreq);
+    if (!ioreq->blkdev->feature_grant_copy) {
+        ioreq_unmap(ioreq);
+    }
     ioreq_finish(ioreq);
     switch (ioreq->req.operation) {
     case BLKIF_OP_WRITE:
@@ -538,8 +664,18 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
 {
     struct XenBlkDev *blkdev = ioreq->blkdev;
 
-    if (ioreq->req.nr_segments && ioreq_map(ioreq) == -1) {
-        goto err_no_map;
+    if (ioreq->blkdev->feature_grant_copy) {
+        ioreq_init_copy_buffers(ioreq);
+        if (ioreq->req.nr_segments && (ioreq->req.operation == BLKIF_OP_WRITE ||
+            ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
+            ioreq_grant_copy(ioreq)) {
+                ioreq_free_copy_buffers(ioreq);
+                goto err;
+        }
+    } else {
+        if (ioreq->req.nr_segments && ioreq_map(ioreq)) {
+            goto err;
+        }
     }
 
     ioreq->aio_inflight++;
@@ -582,6 +718,9 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
     }
     default:
         /* unknown operation (shouldn't happen -- parse catches this) */
+        if (!ioreq->blkdev->feature_grant_copy) {
+            ioreq_unmap(ioreq);
+        }
         goto err;
     }
 
@@ -590,8 +729,6 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
     return 0;
 
 err:
-    ioreq_unmap(ioreq);
-err_no_map:
     ioreq_finish(ioreq);
     ioreq->status = BLKIF_RSP_ERROR;
     return -1;
@@ -1034,6 +1171,12 @@ static int blk_connect(struct XenDevice *xendev)
 
     xen_be_bind_evtchn(&blkdev->xendev);
 
+    blkdev->feature_grant_copy =
+                (xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 0);
+
+    xen_be_printf(&blkdev->xendev, 3, "grant copy operation %s\n",
+                  blkdev->feature_grant_copy ? "enabled" : "disabled");
+
     xen_be_printf(&blkdev->xendev, 1, "ok: proto %s, ring-ref %d, "
                   "remote port %d, local port %d\n",
                   blkdev->xendev.protocol, blkdev->ring_ref,