Re: [PATCH DNA 5/6] tools/xenstored: restore support for mapping ring as foreign memory

[Juergen Gross <jgross@xxxxxxxx>]

On 20.09.21 12:42, Roger Pau Monné wrote:
> On Mon, Sep 20, 2021 at 10:24:45AM +0200, Juergen Gross wrote:
> > On 17.09.21 17:46, Roger Pau Monne wrote:
> > > Restore the previous way of mapping the xenstore ring using foreign
> > > memory. Use xenforeignmemory instead of libxc in order to avoid adding
> > > another dependency on a unstable interface.
> > Mapping a guest page via xenforeignmemory is no good move IMO. A guest
> > not supporting a grant table for security reasons is a rather strange
> > idea, as it needs to trade that for a general memory access by any
> > backend without a way to restrict such accesses. This contradicts one
> > of the main concepts of the Xen security architecture.
> I've done this in order to be able to assert that the switch to
> disable grant tables was working correctly, I don't intended this
> specific mode to be something that is desirable or that should be used
> in production, but I do think it's useful to be able to create such
> guests in order to assert that the option is taking effect.
>
> The main problem of xenstore not being correctly initialized on a
> domain is that the "@introduceDomain" watch doesn't fire, and thus
> other components don't get notified of the newly created domain.
>
> This seems to be a limitation of the current design, where the only
> way to get notifications of new domain creation is using
> "@introduceDomain", even when the caller doesn't care of whether the
> created domain as a working xenstore connection.
>
> Maybe I can workaround this differently in xenstore, so that the watch
> fires even when the shared xenstore ring cannot be initialized.
Yes, I think this would be the way to go.


Juergen

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature
Description: OpenPGP digital signature