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

[Wei Liu <wei.liu2@citrix.com>]

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@citrix.com> 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@citrix.com> 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@eikelenboom.it>
> > > > Signed-off-by: Wei Liu <wei.liu2@citrix.com>  
> > > 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)

Wei.