Re: [Qemu-devel] [PATCH v2 1/2] cpu/apic: drop icc bus/bridge/

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 23 Mar 2015 13:54:23 +0800
Chen Fan <chen.fan.fnst@cn.fujitsu.com> wrote:

> ICC bus was invented only to provide hotplug capability to
> CPU and APIC because at the time being hotplug was available only for
> BUS attached devices.
> 
> Now this patch is to drop ICC bus impl, and switch to bus-less
> CPU+APIC hotplug, handling them in the same manner as pc-dimm.
> 
> Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> ---
>  hw/i386/pc.c                    | 29 +++++++++++------------------
>  hw/i386/pc_piix.c               |  9 +--------
>  hw/i386/pc_q35.c                |  9 +--------
>  hw/intc/apic.c                  |  6 +++---
>  hw/intc/apic_common.c           | 11 ++---------
>  include/hw/i386/apic_internal.h |  5 ++---
>  include/hw/i386/pc.h            |  2 +-
>  target-i386/cpu.c               |  2 --
>  8 files changed, 21 insertions(+), 52 deletions(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 4b46c29..5d15473 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
[...]

> @@ -1093,8 +1083,11 @@ void pc_cpus_init(const char *cpu_model, DeviceState *icc_bridge)
>      /* map APIC MMIO area if CPU has APIC */
>      if (cpu && cpu->apic_state) {
>          /* XXX: what if the base changes? */
> -        sysbus_mmio_map_overlap(SYS_BUS_DEVICE(icc_bridge), 0,
> -                                APIC_DEFAULT_ADDRESS, 0x1000);
> +        apic = APIC_COMMON(cpu->apic_state);
> +        memory_region_add_subregion_overlap(CPU(cpu)->as->root,
> +                                            APIC_DEFAULT_ADDRESS,
> +                                            &apic->io_memory,
> +                                            0x1000);
Why is it here?
Shouldn't it be mapped not once but for each CPU since we are using
per CPU address spaces?

Split this change out into a separate patch please, with commit message
describing what it does.

PS:
It should be part of APIC code or at worst case part of CPU's realize.

PS2:
new cpu tests don't test actual CPU execution, so they can't validate
this change. To test it you need to run test in TCG (at least) or
TCG + KVM mode, with some guest code that programs and checks APIC
of each CPU.

PS3:
the rest of the patch I'd suggest to merge with 2/2 patch that
removes unused icc_bridge code, there isn't point in splitting
that from removing icc_bridge from other files.

[...]
>  
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index f01690b..2385e6b 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -42,7 +42,6 @@
>  
>  #include "sysemu/sysemu.h"
>  #include "hw/qdev-properties.h"
> -#include "hw/cpu/icc_bus.h"
>  #ifndef CONFIG_USER_ONLY
>  #include "hw/xen/xen.h"
>  #include "hw/i386/apic_internal.h"
> @@ -2941,7 +2940,6 @@ static void x86_cpu_common_class_init(ObjectClass *oc, void *data)
>  
>      xcc->parent_realize = dc->realize;
>      dc->realize = x86_cpu_realizefn;
> -    dc->bus_type = TYPE_ICC_BUS;
that isn't the only place in this file that should be changed.

See x86_cpu_apic_create():
  cpu->apic_state = qdev_try_create(qdev_get_parent_bus(dev), apic_type);

probably it's not right to try get parent bus from bus-less device,
qdev_try_create() call should be replaced by object_new()/object_unref() pair.

>      dc->props = x86_cpu_properties;
>  
>      xcc->parent_reset = cc->reset;