Re: [PATCH v2 00/12] Alternate p2m: support multiple copies of host p2m

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 22/06/15 19:56, Ed White wrote:
> This set of patches adds support to hvm domains for EPTP switching by creating
> multiple copies of the host p2m (currently limited to 10 copies).
>
> The primary use of this capability is expected to be in scenarios where access
> to memory needs to be monitored and/or restricted below the level at which the
> guest OS page tables operate. Two examples that were discussed at the 2014 Xen
> developer summit are:
>
>     VM introspection: 
>         http://www.slideshare.net/xen_com_mgr/
>         zero-footprint-guest-memory-introspection-from-xen
>
>     Secure inter-VM communication:
>         http://www.slideshare.net/xen_com_mgr/nakajima-nvf
>
> A more detailed design specification can be found at:
>     http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg01319.html
>
> Each p2m copy is populated lazily on EPT violations.
> Permissions for pages in alternate p2m's can be changed in a similar
> way to the existing memory access interface, and gfn->mfn mappings can be changed.
>
> All this is done through extra HVMOP types.
>
> The cross-domain HVMOP code has been compile-tested only. Also, the cross-domain
> code is hypervisor-only, the toolstack has not been modified.
>
> The intra-domain code has been tested. Violation notifications can only be received
> for pages that have been modified (access permissions and/or gfn->mfn mapping) 
> intra-domain, and only on VCPU's that have enabled notification.
>
> VMFUNC and #VE will both be emulated on hardware without native support.
>
> This code is not compatible with nested hvm functionality and will refuse to work
> with nested hvm active. It is also not compatible with migration. It should be
> considered experimental.

Overall, this patch series is looking very good, and it would seem that
3rd party testing agrees!

~Andrew