Re: [Xen-devel] [RFC PATCH 3/4] x86/p2m : remove checks that forbid adding foreign pages between HVM guests

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Aug 04, 2017 at 10:20:24AM +0800, Zhongze Liu wrote:
> Two checks in the p2m code forbids sharing physical pages among DomU's by 
> using
> xc_add_to_physmap_batch with XENMAPSPACE_gmfn_foreign. Just simply remove them
> in this RFC patch to ask for suggestions on how to properly handle this.
> 
> This is for the proposal "Allow setting up shared memory areas between VMs
> from xl config file" (see [1]).
> 
> [1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html
> 
> Signed-off-by: Zhongze Liu <blackskygg@xxxxxxxxx>
> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxx
> ---
>  xen/arch/x86/mm/p2m.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index e8a57d118c..3ee4c14ed4 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -2531,8 +2531,13 @@ int p2m_add_foreign(struct domain *tdom, unsigned long 
> fgfn,
>       * hvm fixme: until support is added to p2m teardown code to cleanup any
>       * foreign entries, limit this to hardware domain only.

This HVM fixme needs to be fixed before the check can go away. This is
going to be a non-trivial project, but it is going to be useful in its
own right.

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