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

[Anthony PERARD]

On Thu, Apr 02, 2020 at 02:29:25PM +0200, Igor Mammedov wrote:
> On Mon, 30 Mar 2020 17:52:48 +0100
> Anthony PERARD <address@hidden> 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 <address@hidden>
> > > Signed-off-by: Igor Mammedov <address@hidden>  
> > 
> > Reviewed-by: Anthony PERARD <address@hidden>
> > 
> > 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;

After fixing the build issues, it does work, yes. I've tested both "xenfv"
and "pc,accel=xen".

Build issue:
- I've added #include "hw/boards.h"
- and s/m->/mc->/

Thanks!

-- 
Anthony PERARD