Re: [PATCH for-5.0 v2] xen: fixup RAM memory region initialization

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 2 Apr 2020 20:57:14 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 02/04/20 16:54, Igor Mammedov wrote:
> > Since bd457782b3b0 ("x86/pc: use memdev for RAM") Xen
> > machine fails to start with:
> >    qemu-system-i386: xen: failed to populate ram at 0
> > 
> > The reason is that xen_ram_alloc() which is called by
> > memory_region_init_ram(), compares memory region with
> > statically allocated 'global' ram_memory memory region
> > that it uses for RAM, and does nothing in case it matches.
> > 
> > While it's possible feed machine->ram to xen_ram_alloc()
> > in the same manner to keep that hack working, I'd prefer
> > not to keep that circular dependency and try to untangle that.
> > 
> > However it doesn't look trivial to fix, so as temporary
> > fixup opt out Xen machine from memdev based RAM allocation,
> > and let xen_ram_alloc() do its trick for now.
> > 
> > Reported-by: Anthony PERARD <anthony.perard@citrix.com>
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > v2:
> >   * make it work with -M pc,accel=xen
> > ---
> >  hw/xen/xen-common.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
> > index 15650d7f6a..a15070f7f6 100644
> > --- a/hw/xen/xen-common.c
> > +++ b/hw/xen/xen-common.c
> > @@ -19,6 +19,7 @@
> >  #include "sysemu/runstate.h"
> >  #include "migration/misc.h"
> >  #include "migration/global_state.h"
> > +#include "hw/boards.h"
> >  
> >  //#define DEBUG_XEN
> >  
> > @@ -151,6 +152,8 @@ static void xen_setup_post(MachineState *ms, AccelState *accel)
> >  
> >  static int xen_init(MachineState *ms)
> >  {
> > +    MachineClass *mc = MACHINE_GET_CLASS(ms);
> > +
> >      xen_xc = xc_interface_open(0, 0, 0);
> >      if (xen_xc == NULL) {
> >          xen_pv_printf(NULL, 0, "can't open xen interface\n");
> > @@ -170,6 +173,10 @@ static int xen_init(MachineState *ms)
> >          return -1;
> >      }
> >      qemu_add_vm_change_state_handler(xen_change_state_handler, NULL);
> > +    /*
> > +     * opt out of system RAM being allocated by generic code
> > +     */
> > +    mc->default_ram_id = NULL;
> >      return 0;
> >  }
> >  
> >   
> 
> Monkey patching the class is slightly disgusting. :)  It would be better
> to use a new ms->default_ram_id, and assign it from the class in
> instance_init, but I've queued it anyway.

it's disgusting, I hope to drop this after fixing xen properly.

> 
> Paolo
> 
>