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

[Stefano Stabellini]

On Wed, 26 Oct 2016, Stefano Stabellini wrote:
> On Wed, 26 Oct 2016, Wei Liu 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 <address@hidden> 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 <address@hidden>
> > > > Signed-off-by: Wei Liu <address@hidden>
> > > 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.
> 
> What if libxl passes -no-acpi to QEMU?

Of course even if that works, I think we should still fix this properly
in QEMU


> > > > ---
> > > > Cc: Anthony PERARD <address@hidden>
> > > > Cc: Stefano Stabellini <address@hidden>
> > > > 
> > > > RFC because I'm not sure this is the best way to fix it.
> > > > ---
> > > >  hw/i386/acpi-build.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > > > index a26a4bb..2cdff12 100644
> > > > --- a/hw/i386/acpi-build.c
> > > > +++ b/hw/i386/acpi-build.c
> > > > @@ -45,6 +45,7 @@
> > > >  #include "sysemu/tpm_backend.h"
> > > >  #include "hw/timer/mc146818rtc_regs.h"
> > > >  #include "sysemu/numa.h"
> > > > +#include "hw/xen/xen.h"
> > > >  
> > > >  /* Supported chipsets: */
> > > >  #include "hw/acpi/piix4.h"
> > > > @@ -2865,6 +2866,11 @@ void acpi_setup(void)
> > > >          return;
> > > >      }
> > > >  
> > > > +    if (xen_enabled()) {
> > > > +        ACPI_BUILD_DPRINTF("Xen enabled. Bailing out.\n");
> > > > +        return;
> > > > +    }
> > > > +
> > > >      build_state = g_malloc0(sizeof *build_state);
> > > >  
> > > >      acpi_set_pci_info();
> > > 
> > 
>