Re: [Xen-devel] [Qemu-devel] [PATCH RFC] acpi: don't build acpi tables for xen hvm guests

[Igor Mammedov <imammedo@xxxxxxxxxx>]

On Thu, 27 Oct 2016 12:10:58 +0100
Wei Liu <wei.liu2@xxxxxxxxxx> wrote:

> On Thu, Oct 27, 2016 at 12:03:42PM +0100, Wei Liu wrote:
> > Cc Sander
> > 
> > On Thu, Oct 27, 2016 at 12:54:02PM +0200, Igor Mammedov wrote:  
> > > On Wed, 26 Oct 2016 16:22:34 +0100
> > > Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> > >   
> > > > On Wed, Oct 26, 2016 at 05:09:52PM +0200, Igor Mammedov wrote:  
> > > > > On Tue, 25 Oct 2016 18:28:04 +0100
> > > > > Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> > > > >     
> > > > > > Xen's toolstack is in charge of building ACPI tables. Skip acpi 
> > > > > > table
> > > > > > building if running on Xen.
> > > > > > 
> > > > > > This issue is discovered due to direct kernel boot on Xen doesn't 
> > > > > > boot
> > > > > > anymore, because the new ACPI tables cause the guest to exceed its
> > > > > > memory allocation limit.
> > > > > > 
> > > > > > Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> > > > > > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>    
> > > > > Question is:
> > > > > Why does xen guest get ACPI tables from QEMU instead of using
> > > > > Xen provided ones.
> > > > > Maybe it's firmware issue i.e. firmware side shouldn't load
> > > > > ACPI tables from QEMU provided fwcfg file and load Xen provided 
> > > > > instead.
> > > > >     
> > > > 
> > > > It hasn't come to the point that the guest is booted. QEMU exits when
> > > > trying to populate some pages for the guest, at which point the guest
> > > > has not yet been started.  In a sense, Xen guest doesn't get ACPI from
> > > > QEMU because it never gets to that point.
> > > > 
> > > > Direct kernel boot causes fw_cfg to be filled in. pcms->has_acpi_build
> > > > defaults to true and acpi_enabled is also true. These make all checks in
> > > > acpi_setup pass. QEMU proceeds to build and load ACPI tables (which are
> > > > never going to be used by Xen guests), causing the guest to exceeds its
> > > > limit.
> > > > 
> > > > Wei.  
> > > Would something like this fix issue for you?
> > > 
> > > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > > index a54a468..61b6026 100644
> > > --- a/hw/i386/pc_piix.c
> > > +++ b/hw/i386/pc_piix.c
> > > @@ -1094,10 +1094,13 @@ DEFINE_PC_MACHINE(isapc, "isapc", pc_init_isa,
> > >  #ifdef CONFIG_XEN
> > >  static void xenfv_machine_options(MachineClass *m)
> > >  {
> > > +    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
> > > +
> > >      m->desc = "Xen Fully-virtualized PC";
> > >      m->max_cpus = HVM_MAX_VCPUS;
> > >      m->default_machine_opts = "accel=xen";
> > >      m->hot_add_cpu = pc_hot_add_cpu;
> > > +    pcmc->has_acpi_build = false;
> > >  }
> > >  
> > >  DEFINE_PC_MACHINE(xenfv, "xenfv", pc_xen_hvm_init,
> > >   
> > 
> > Yes, it does.
> > 
> > (I have a similar patch in my queue already)
> >   
> 
> Oh, the reason I didn't send it out is because Eduardo suggested we
> should use a new field instead of setting has_acpi_build outside of
> PCMachineClass init function.
> 
> I have actually gotten around to investigate this option and what is
> needed to be done.
static void xenfv_machine_options(MachineClass *m)                              
 
{                                                                               
 
...                                              
}                                                                               
 
                                                                                
 
DEFINE_PC_MACHINE(xenfv, "xenfv", pc_xen_hvm_init,                              
 
                  xenfv_machine_options);      

#define DEFINE_PC_MACHINE(suffix, namestr, initfn, optsfn) \                    
 
    static void pc_machine_##suffix##_class_init(ObjectClass *oc, void *data) \ 
 
    { \                                                                         
 
        MachineClass *mc = MACHINE_CLASS(oc); \                                 
 
        optsfn(mc); \                                                           
 
        mc->init = initfn; \                                                    
 
    } \  
...

So xenfv_machine_options() is a part of pc_machine_xenfv_class_init()

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