[Xen-devel] [RFC PATCH 16/16] xen/grant-table: host_addr fixup in mapping on xenhost_r0

[Ankur Arora <ankur.a.arora@xxxxxxxxxx>]

Xenhost type xenhost_r0 does not support standard GNTTABOP_map_grant_ref
semantics (map a gref onto a specified host_addr). That's because
since the hypervisor is local (same address space as the caller of
GNTTABOP_map_grant_ref), there is no external entity that could
map an arbitrary page underneath an arbitrary address.

To handle this, the GNTTABOP_map_grant_ref hypercall on xenhost_r0
treats the host_addr as an OUT parameter instead of IN and expects the
gnttab_map_refs() and similar to fixup any state that caches the
value of host_addr from before the hypercall.

Accordingly gnttab_map_refs() now adds two parameters, a fixup function
and a pointer to cached maps to fixup:
 int gnttab_map_refs(xenhost_t *xh, struct gnttab_map_grant_ref *map_ops,
                    struct gnttab_map_grant_ref *kmap_ops,
-                   struct page **pages, unsigned int count)
+                   struct page **pages, gnttab_map_fixup_t map_fixup_fn,
+                   void **map_fixup[], unsigned int count)

The reason we use a fixup function and not an additional mapping op
in the xenhost_t is because, depending on the caller, what we are fixing
might be different: blkback, netback for instance cache host_addr in
via a struct page *, while __xenbus_map_ring() caches a phys_addr.

This patch fixes up xen-blkback and xen-gntdev drivers.

TODO:
  - also rewrite gnttab_batch_map() and __xenbus_map_ring().
  - modify xen-netback, scsiback, pciback etc

Co-developed-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
 drivers/block/xen-blkback/blkback.c | 14 +++++++++++++-
 drivers/xen/gntdev.c                |  2 +-
 drivers/xen/grant-table.c           | 20 ++++++++++++++------
 include/xen/grant_table.h           | 11 ++++++++++-
 4 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c 
b/drivers/block/xen-blkback/blkback.c
index d366a17a4bd8..50ce40ba35e5 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -806,11 +806,18 @@ static void xen_blkbk_unmap(struct xen_blkif_ring *ring,
        }
 }
 
+static void blkbk_map_fixup(uint64_t host_addr, void **fixup)
+{
+       struct page **pg = (struct page **)fixup;
+       *pg = virt_to_page(host_addr);
+}
+
 static int xen_blkbk_map(struct xen_blkif_ring *ring,
                         struct grant_page *pages[],
                         int num, bool ro)
 {
        struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+       struct page **map_fixup[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct page *pages_to_gnt[BLKIF_MAX_SEGMENTS_PER_REQUEST];
        struct persistent_gnt *persistent_gnt = NULL;
        phys_addr_t addr = 0;
@@ -858,6 +865,9 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
                        gnttab_set_map_op(&map[segs_to_map++], addr,
                                          flags, pages[i]->gref,
                                          blkif->domid);
+
+                       if (gnttab_map_fixup(dev->xh))
+                                 map_fixup[i] = &pages[i]->page;
                }
                map_until = i + 1;
                if (segs_to_map == BLKIF_MAX_SEGMENTS_PER_REQUEST)
@@ -865,7 +875,9 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
        }
 
        if (segs_to_map) {
-               ret = gnttab_map_refs(dev->xh, map, NULL, pages_to_gnt, 
segs_to_map);
+               ret = gnttab_map_refs(dev->xh, map, NULL, pages_to_gnt,
+                       gnttab_map_fixup(dev->xh) ? blkbk_map_fixup : NULL,
+                                       (void ***) map_fixup, segs_to_map);
                BUG_ON(ret);
        }
 
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 40a42abe2dd0..32c6471834ba 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -342,7 +342,7 @@ int gntdev_map_grant_pages(struct gntdev_grant_map *map)
 
        pr_debug("map %d+%d\n", map->index, map->count);
        err = gnttab_map_refs(xh, map->map_ops, use_ptemod ? map->kmap_ops : 
NULL,
-                       map->pages, map->count);
+                       map->pages, NULL, NULL, map->count);
        if (err)
                return err;
 
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 959b81ade113..2f3a0a4a2660 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -1084,7 +1084,8 @@ void gnttab_foreach_grant(struct page **pages,
 
 int gnttab_map_refs(xenhost_t *xh, struct gnttab_map_grant_ref *map_ops,
                    struct gnttab_map_grant_ref *kmap_ops,
-                   struct page **pages, unsigned int count)
+                   struct page **pages, gnttab_map_fixup_t map_fixup_fn,
+                   void **map_fixup[], unsigned int count)
 {
        int i, ret;
 
@@ -1096,12 +1097,19 @@ int gnttab_map_refs(xenhost_t *xh, struct 
gnttab_map_grant_ref *map_ops,
                switch (map_ops[i].status) {
                case GNTST_okay:
                {
-                       struct xen_page_foreign *foreign;
+                       if (!gnttab_map_fixup(xh)) {
+                               struct xen_page_foreign *foreign;
 
-                       SetPageForeign(pages[i]);
-                       foreign = xen_page_foreign(pages[i]);
-                       foreign->domid = map_ops[i].dom;
-                       foreign->gref = map_ops[i].ref;
+                               SetPageForeign(pages[i]);
+                               foreign = xen_page_foreign(pages[i]);
+                               foreign->domid = map_ops[i].dom;
+                               foreign->gref = map_ops[i].ref;
+                       } else {
+                               pages[i] = virt_to_page(map_ops[i].host_addr);
+
+                               if (map_fixup_fn)
+                                       map_fixup_fn(map_ops[i].host_addr, 
map_fixup[i]);
+                       }
                        break;
                }
 
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index 827b790199fb..14f7cc70cd01 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -219,9 +219,18 @@ int gnttab_dma_free_pages(xenhost_t *xh, struct 
gnttab_dma_alloc_args *args);
 int gnttab_pages_set_private(int nr_pages, struct page **pages);
 void gnttab_pages_clear_private(int nr_pages, struct page **pages);
 
+static inline bool
+gnttab_map_fixup(xenhost_t *xh)
+{
+       return xh->type == xenhost_r0;
+}
+
+typedef void (*gnttab_map_fixup_t)(uint64_t host_addr, void **map_fixup);
+
 int gnttab_map_refs(xenhost_t *xh, struct gnttab_map_grant_ref *map_ops,
                    struct gnttab_map_grant_ref *kmap_ops,
-                   struct page **pages, unsigned int count);
+                   struct page **pages, gnttab_map_fixup_t map_fixup_fn,
+                   void **map_fixup[], unsigned int count);
 int gnttab_unmap_refs(xenhost_t *xh, struct gnttab_unmap_grant_ref *unmap_ops,
                      struct gnttab_unmap_grant_ref *kunmap_ops,
                      struct page **pages, unsigned int count);
-- 
2.20.1


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