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

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

On 6/17/19 3:55 AM, Juergen Gross wrote:
> 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.
> >
> > 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>
> Without seeing the __xenbus_map_ring() modification it is impossible to
> do a proper review of this patch.
Will do in v2.

Ankur

> Juergen
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