Re: [Xen-devel] [PATCH] grant table and bogus mfns

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 12/11/07 09:35, "Kieran Mansley" <kmansley@xxxxxxxxxxxxxx> wrote:

>  1) dom0 does a grant op for a page of I/O memory; at this stage no
> different to a normal grant.
>  2) grant reference passed (e.g. through xenstore) to domU
>  3) domU performs a map operation on that grant
>  4) hypervisor notices that the grant is for an I/O memory page and
> instead of mapping it to a domU virtual address it instead sets up the
> I/O mem permissions for that domain to access the region (ie. calls
> iomem_permit_access())
>  5) domU can then call ioremap() to get a kernel virtual address for the
> I/O memory region, and access it as normal.

I didn't realise this was how it worked. I think it's a bad idea -- mapping
the grantref should map the I/O page. The mapping domain's io capabilities
should not be affected. Apart from being the obvious semantics for
map_grant, using the current scheme we cannot be sure when all mappings to
the granted page have gone away.

 -- Keir



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