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SubjectRe: [RFC PATCH 16/16] xen/grant-table: host_addr fixup in mapping on xenhost_r0
On 09.05.19 19:25, Ankur Arora wrote:
> 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.
> - also rewrite gnttab_batch_map() and __xenbus_map_ring().
> - modify xen-netback, scsiback, pciback etc
> Co-developed-by: Joao Martins <>
> Signed-off-by: Ankur Arora <>

Without seeing the __xenbus_map_ring() modification it is impossible to
do a proper review of this patch.


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