Re: [PATCH v2 09/17] xen/dom0less: store xenstore event channel in page

[Jürgen Groß <jgross@xxxxxxxx>]

On 17.07.25 08:25, Jan Beulich wrote:
> On 17.07.2025 08:19, Juergen Gross wrote:
> > On 16.07.25 23:14, Jason Andryuk wrote:
> > > Write the associated event channel into the xenstore page so xenstored
> > > can read it.  xenstored can map the grant by the reserved grant table
> > > entry, and then read out the event channel and bind it.  This eliminates
> > > the need for an additional mechanism to discover the event channel.
> > >
> > > Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> > > ---
> > >    xen/common/device-tree/dom0less-build.c | 7 +++++++
> > >    1 file changed, 7 insertions(+)
> > >
> > > diff --git a/xen/common/device-tree/dom0less-build.c 
> > > b/xen/common/device-tree/dom0less-build.c
> > > index a2789e3bdf..284139bf14 100644
> > > --- a/xen/common/device-tree/dom0less-build.c
> > > +++ b/xen/common/device-tree/dom0less-build.c
> > > @@ -26,6 +26,7 @@
> > >    #include <public/io/xs_wire.h>
> > >    
> > >    #include <asm/dom0less-build.h>
> > > +#include <asm/guest_access.h>
> > >    #include <asm/setup.h>
> > >    
> > >    #include <xen/static-memory.h>
> > > @@ -126,8 +127,14 @@ static void __init initialize_domU_xenstore(void)
> > >    
> > >            if ( gfn != XENSTORE_PFN_LATE_ALLOC && IS_ENABLED(CONFIG_GRANT_TABLE) )
> > >            {
> > > +            evtchn_port_t port = d->arch.hvm.params[HVM_PARAM_STORE_EVTCHN];
> > > +            paddr_t evtchn_gaddr = gfn_to_gaddr(_gfn(gfn)) +
> > > +                offsetof(struct xenstore_domain_interface, evtchn_port);
> > > +
> > >                ASSERT(gfn < UINT32_MAX);
> > >                gnttab_seed_entry(d, GNTTAB_RESERVED_XENSTORE, xs_domid, gfn);
> > > +            access_guest_memory_by_gpa(d, evtchn_gaddr, &port, sizeof(port),
> > > +                                       true /* is_write */);
> > I couldn't find access_guest_memory_by_gpa() for x86. I think you either need to
> > introduce it for all archs, or you need to handle this differently.
> This code isn't buildable (yet) for x86, is it? There's a series of Alejandro's
> moving in that direction, but that didn't go in yet. And even then aiui this
> file would still be excluded.
I think this would need to be explicitly mentioned in the commit message
then. I thought this whole work would be targeting x86 as well, but I
might be wrong, of course.


Juergen

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