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Subject[RFC PATCH 16/16] xen/grant-table: host_addr fixup in mapping on xenhost_r0
Date
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@oracle.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
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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