Re: [Qemu-devel] [PATCHv2 3/4] cpuid: disable pv eoi for 1.1 and older compat types

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 28, 2012 at 04:40:38PM -0300, Eduardo Habkost wrote:
> On Tue, Aug 28, 2012 at 02:13:18PM -0500, Anthony Liguori wrote:
> > "Michael S. Tsirkin" <mst@redhat.com> writes:
> > 
> > > In preparation for adding PV EOI support, disable PV EOI by default for
> > > 1.1 and older machine types, to avoid CPUID changing during migration.
> > >
> > > PV EOI can still be enabled/disabled by specifying it explicitly.
> > >     Enable for 1.1
> > >     -M pc-1.1 -cpu kvm64,+kvm_pv_eoi
> > >     Disable for 1.2
> > >     -M pc-1.2 -cpu kvm64,-kvm_pv_eoi
> > >
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > >  hw/Makefile.objs  |  2 +-
> > >  hw/cpu_flags.c    | 32 ++++++++++++++++++++++++++++++++
> > >  hw/cpu_flags.h    |  9 +++++++++
> > >  hw/pc_piix.c      |  2 ++
> > >  target-i386/cpu.c |  8 ++++++++
> > >  5 files changed, 52 insertions(+), 1 deletion(-)
> > >  create mode 100644 hw/cpu_flags.c
> > >  create mode 100644 hw/cpu_flags.h
> > >
> > > diff --git a/hw/Makefile.objs b/hw/Makefile.objs
> > > index 850b87b..3f2532a 100644
> > > --- a/hw/Makefile.objs
> > > +++ b/hw/Makefile.objs
> > > @@ -1,5 +1,5 @@
> > >  hw-obj-y = usb/ ide/
> > > -hw-obj-y += loader.o
> > > +hw-obj-y += loader.o cpu_flags.o
> > >  hw-obj-$(CONFIG_VIRTIO) += virtio-console.o
> > >  hw-obj-$(CONFIG_VIRTIO_PCI) += virtio-pci.o
> > >  hw-obj-y += fw_cfg.o
> > > diff --git a/hw/cpu_flags.c b/hw/cpu_flags.c
> > > new file mode 100644
> > > index 0000000..2422d20
> > > --- /dev/null
> > > +++ b/hw/cpu_flags.c
> > > @@ -0,0 +1,32 @@
> > > +/*
> > > + * CPU compatibility flags.
> > > + *
> > > + * Copyright (c) 2012 Red Hat Inc.
> > > + * Author: Michael S. Tsirkin.
> > > + *
> > > + * This program is free software; you can redistribute it and/or modify
> > > + * it under the terms of the GNU General Public License as published by
> > > + * the Free Software Foundation; either version 2 of the License, or
> > > + * (at your option) any later version.
> > > + *
> > > + * This program is distributed in the hope that it will be useful,
> > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > > + * GNU General Public License for more details.
> > > + *
> > > + * You should have received a copy of the GNU General Public License along
> > > + * with this program; if not, see <http://www.gnu.org/licenses/>.
> > > + */
> > > +#include "hw/cpu_flags.h"
> > > +
> > > +static bool __kvm_pv_eoi_disabled;
> > > +
> > > +void disable_kvm_pv_eoi(void)
> > > +{
> > > +       __kvm_pv_eoi_disabled = true;
> > > +}
> > > +
> > > +bool kvm_pv_eoi_disabled(void)
> > > +{
> > > +       return __kvm_pv_eoi_disabled;
> > > +}
> > 
> > Would this make more sense as a CPU flag or at least the KVM PV LAPIC?
> 
> It is a CPU flag, already. The problem is that QEMU defaults to enabling
> blindly everything reported by the host kernel, potentially breaking
> migration (and this still has to be fixed).
> > 
> > We really ought to embed the LAPIC in the CPU objects.  Then it would
> > all make a bit more sense conceptionally.  But I definitely thing a CPU
> > feature flag makes the most sense here.
> > 
> > Then we can handle it via globals once we make CPU's qdev devices.
> 
> Yes, this is a perfect candidate to use globals/qdev for machine-type
> compatibility.

OK so ... ACK?

> > 
> > Regards,
> > 
> > Anthony Liguori
> > 
> > > diff --git a/hw/cpu_flags.h b/hw/cpu_flags.h
> > > new file mode 100644
> > > index 0000000..05777b6
> > > --- /dev/null
> > > +++ b/hw/cpu_flags.h
> > > @@ -0,0 +1,9 @@
> > > +#ifndef HW_CPU_FLAGS_H
> > > +#define HW_CPU_FLAGS_H
> > > +
> > > +#include <stdbool.h>
> > > +
> > > +void disable_kvm_pv_eoi(void);
> > > +bool kvm_pv_eoi_disabled(void);
> > > +
> > > +#endif
> > > diff --git a/hw/pc_piix.c b/hw/pc_piix.c
> > > index 008d42f..bdbceda 100644
> > > --- a/hw/pc_piix.c
> > > +++ b/hw/pc_piix.c
> > > @@ -46,6 +46,7 @@
> > >  #ifdef CONFIG_XEN
> > >  #  include <xen/hvm/hvm_info_table.h>
> > >  #endif
> > > +#include "cpu_flags.h"
> > >  
> > >  #define MAX_IDE_BUS 2
> > >  
> > > @@ -371,6 +372,7 @@ static QEMUMachine pc_machine_v1_2 = {
> > >  
> > >  static void pc_machine_v1_1_compat(void)
> > >  {
> > > +    disable_kvm_pv_eoi();
> > >  }
> > >  
> > >  static void pc_init_pci_v1_1(ram_addr_t ram_size,
> > > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > > index 120a2e3..0d02fd1 100644
> > > --- a/target-i386/cpu.c
> > > +++ b/target-i386/cpu.c
> > > @@ -23,6 +23,7 @@
> > >  
> > >  #include "cpu.h"
> > >  #include "kvm.h"
> > > +#include "asm/kvm_para.h"
> > >  
> > >  #include "qemu-option.h"
> > >  #include "qemu-config.h"
> > > @@ -33,6 +34,7 @@
> > >  #include "hyperv.h"
> > >  
> > >  #include "hw/hw.h"
> > > +#include "hw/cpu_flags.h"
> > >  
> > >  /* feature flags taken from "Intel Processor Identification and the CPUID
> > >   * Instruction" and AMD's "CPUID Specification".  In cases of disagreement
> > > @@ -889,6 +891,12 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, const char *cpu_model)
> > >  
> > >      plus_kvm_features = ~0; /* not supported bits will be filtered out later */
> > >  
> > > +    /* Disable PV EOI for old machine types.
> > > +     * Feature flags can still override. */
> > > +    if (kvm_pv_eoi_disabled()) {
> > > +        plus_kvm_features &= ~(0x1 << KVM_FEATURE_PV_EOI);
> > > +    }
> > > +
> > >      add_flagname_to_bitmaps("hypervisor", &plus_features,
> > >          &plus_ext_features, &plus_ext2_features, &plus_ext3_features,
> > >          &plus_kvm_features, &plus_svm_features);
> > > -- 
> > > MST
> > 
> 
> -- 
> Eduardo