Re: [Xen-devel] [PATCH 3/3] xen-netback: handle page straddling in xenvif_set_hash_mapping()

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 28 August 2018 16:00
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: davem@xxxxxxxxxxxxx; xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>;
> netdev@xxxxxxxxxxxxxxx
> Subject: [PATCH 3/3] xen-netback: handle page straddling in
> xenvif_set_hash_mapping()
> 
> There's no guarantee that the mapping array doesn't cross a page
> boundary. Use a second grant copy operation if necessary.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Personally I think it would be cleaner to out-of-line the allocation of the 
mapping table and ensure it is page aligned but this works so...

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> 
> ---
>  drivers/net/xen-netback/hash.c |   25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
> 
> --- 4.19-rc1-xen-netback-set-hash-mapping.orig/drivers/net/xen-
> netback/hash.c
> +++ 4.19-rc1-xen-netback-set-hash-mapping/drivers/net/xen-
> netback/hash.c
> @@ -334,28 +334,39 @@ u32 xenvif_set_hash_mapping(struct xenvi
>                           u32 off)
>  {
>       u32 *mapping = vif->hash.mapping[!vif->hash.mapping_sel];
> -     struct gnttab_copy copy_op = {
> +     unsigned int nr = 1;
> +     struct gnttab_copy copy_op[2] = {{
>               .source.u.ref = gref,
>               .source.domid = vif->domid,
>               .dest.domid = DOMID_SELF,
>               .len = len * sizeof(*mapping),
>               .flags = GNTCOPY_source_gref
> -     };
> +     }};
> 
>       if ((off + len < off) || (off + len > vif->hash.size) ||
>           len > XEN_PAGE_SIZE / sizeof(*mapping))
>               return XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;
> 
> -     copy_op.dest.u.gmfn = virt_to_gfn(mapping + off);
> -     copy_op.dest.offset = xen_offset_in_page(mapping + off);
> +     copy_op[0].dest.u.gmfn = virt_to_gfn(mapping + off);
> +     copy_op[0].dest.offset = xen_offset_in_page(mapping + off);
> +     if (copy_op[0].dest.offset + copy_op[0].len > XEN_PAGE_SIZE) {
> +             copy_op[1] = copy_op[0];
> +             copy_op[1].source.offset = XEN_PAGE_SIZE -
> copy_op[0].dest.offset;
> +             copy_op[1].dest.u.gmfn = virt_to_gfn(mapping + off + len);
> +             copy_op[1].dest.offset = 0;
> +             copy_op[1].len = copy_op[0].len - copy_op[1].source.offset;
> +             copy_op[0].len = copy_op[1].source.offset;
> +             nr = 2;
> +     }
> 
>       memcpy(mapping, vif->hash.mapping[vif->hash.mapping_sel],
>              vif->hash.size * sizeof(*mapping));
> 
> -     if (copy_op.len != 0) {
> -             gnttab_batch_copy(&copy_op, 1);
> +     if (copy_op[0].len != 0) {
> +             gnttab_batch_copy(copy_op, nr);
> 
> -             if (copy_op.status != GNTST_okay)
> +             if (copy_op[0].status != GNTST_okay ||
> +                 copy_op[nr - 1].status != GNTST_okay)
>                       return
> XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;
>       }
> 
> 
> 
> 


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