Re: [Xen-devel] [PATCH v2] xen: allow guest_remove_page to remove p2m_mmio_direct pages

[Tim Deegan <tim@xxxxxxx>]

At 16:45 +0200 on 19 Jun (1403192739), Roger Pau Monne wrote:
> IF a guest tries to do a foreign/grant mapping in a memory region
> marked as p2m_mmio_direct Xen will complain with the following
> message:
> 
> (XEN) memory.c:241:d0v0 Bad page free for domain 0
> 
> Albeit the mapping will succeed. This is specially problematic for PVH
> Dom0, in which we map all the e820 holes and memory up to 4GB as
> p2m_mmio_direct.
> 
> In order to deal with it, add a special casing for p2m_mmio_direct
> regions in guest_remove_page if the domain is a hardware domain, that
> calls clear_mmio_p2m_entry in order to remove the mappings.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Acked-by: Tim Deegan <tim@xxxxxxx>

as being an improvement on what's there right now.  But as I said, I
think code that relies on this is probably doing the wrong thing -- in
this case having MMIOmaps og all non-RAM areas seems wrong; dom0 ought
to know what addresses are really hardware and map them appropriately.

Tim.

> ---
> Changes since v1:
>  - Remove the is_hardware_domain check.
> ---
>  xen/common/memory.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/xen/common/memory.c b/xen/common/memory.c
> index 257f4b0..c2dd31b 100644
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -204,6 +204,12 @@ int guest_remove_page(struct domain *d, unsigned long 
> gmfn)
>          p2m_mem_paging_drop_page(d, gmfn, p2mt);
>          return 1;
>      }
> +    if ( p2mt == p2m_mmio_direct )
> +    {
> +        clear_mmio_p2m_entry(d, gmfn);
> +        put_gfn(d, gmfn);
> +        return 1;
> +    }
>  #else
>      mfn = gmfn_to_mfn(d, gmfn);
>  #endif
> -- 
> 1.7.7.5 (Apple Git-26)
> 

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