xen-blkback: xen_shim_domain() support

With xen_shim_domain() enabled, the struct pages used for grant mappings
are only valid in the interval between GNTTABOP_map_grant_ref and
GNTTABOP_unmap_grant_ref.

Ensure that we do not cache the struct page outside that duration.

Also, update the struct page for the segment after
GNTTABOP_map_grant_ref, for the subsequent tracking or when doing IO.

In addition, we disable persistent grants for this configuration, since
the map/unmap overhead is fairly small (in the fast path, page lookup,
get_page() and put_page().) This reduces the memory usage in
blkback/blkfront.

Co-developed-by: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index d51d88be88e14e39161a549c720bf3604a4a822a..20c15e6787b18d9ff5322824abea7335c35bd3d4 100644 (file)
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -167,6 +167,15 @@ static inline void put_free_pages(struct xen_blkif_ring *ring, struct page **pag
        unsigned long flags;
        int i;
 
+       /*
+        * We don't own the struct page after unmap has been called.
+        * Reallocation is cheap anyway for the shim domain case, so free it.
+        */
+       if (xen_shim_domain()) {
+               gnttab_free_pages(num, page);
+               return;
+       }
+
        spin_lock_irqsave(&ring->free_pages_lock, flags);
        for (i = 0; i < num; i++)
                list_add(&page[i]->lru, &ring->free_pages);
@@ -825,7 +834,7 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
         */
 again:
        for (i = map_until; i < num; i++) {
-               uint32_t flags;
+               uint32_t flags = 0;
 
                if (use_persistent_gnts) {
                        persistent_gnt = get_persistent_gnt(
@@ -846,7 +855,8 @@ again:
                        addr = vaddr(pages[i]->page);
                        pages_to_gnt[segs_to_map] = pages[i]->page;
                        pages[i]->persistent_gnt = NULL;
-                       flags = GNTMAP_host_map;
+                       if (!xen_shim_domain())
+                               flags = GNTMAP_host_map;
                        if (!use_persistent_gnts && ro)
                                flags |= GNTMAP_readonly;
                        gnttab_set_map_op(&map[segs_to_map++], addr,
@@ -880,6 +890,8 @@ again:
                                goto next;
                        }
                        pages[seg_idx]->handle = map[new_map_idx].handle;
+                       if (xen_shim_domain())
+                               pages[seg_idx]->page = pages_to_gnt[new_map_idx];
                } else {
                        continue;
                }
@@ -1478,7 +1490,7 @@ static int __init xen_blkif_init(void)
 {
        int rc = 0;
 
-       if (!xen_domain())
+       if (!xen_domain() && !xen_shim_domain_get())
                return -ENODEV;
 
        if (xen_blkif_max_ring_order > XENBUS_MAX_RING_GRANT_ORDER) {
@@ -1508,6 +1520,7 @@ static void __exit xen_blkif_exit(void)
 {
        xen_blkif_interface_exit();
        xen_blkif_xenbus_exit();
+       xen_shim_domain_put();
 }
 
 module_exit(xen_blkif_exit);

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 424e2efebe855ade6a07193021599b9895dfadd1..11be0c052b7753721cda2417f4138f6db12acb8d 100644 (file)
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -871,7 +871,8 @@ again:
 
        xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
 
-       err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
+       err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
+                           !xen_shim_domain());
        if (err) {
                xenbus_dev_fatal(dev, err, "writing %s/feature-persistent",
                                 dev->nodename);
@@ -1059,7 +1060,7 @@ static int connect_ring(struct backend_info *be)
        }
        pers_grants = xenbus_read_unsigned(dev->otherend, "feature-persistent",
                                           0);
-       be->blkif->vbd.feature_gnt_persistent = pers_grants;
+       be->blkif->vbd.feature_gnt_persistent = pers_grants && !xen_shim_domain();
        be->blkif->vbd.overflow_max_grants = 0;
 
        /*