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

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 30 Mar 2020 17:52:48 +0100
Anthony PERARD <anthony.perard@citrix.com> wrote:

> On Fri, Mar 27, 2020 at 06:48:28AM -0400, 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>  
> 
> Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
> 
> That should work on most configs. But we also sometime use the "pc"
> machine with accel=xen, to run without the "xen-platform" pci device,
> but that would be less common.

does following work for you in case of pc machine?

diff --git a/hw/xen/xen-common.c b/hw/xen/xen-common.c
index 15650d7f6a..f19c0883ae 100644
--- a/hw/xen/xen-common.c
+++ b/hw/xen/xen-common.c
@@ -151,6 +151,8 @@ 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 +172,10 @@ 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
+     */
+    m->default_ram_id = NULL;
     return 0;
 }


> Thanks,
>