Re: [Qemu-devel] [PATCH 2/2] pc: acpi-build: make linker & RSDP tables dynamic

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

On Wed, Dec 10, 2014 at 05:45:58PM +0100, Igor Mammedov wrote:
> On Wed, 10 Dec 2014 18:24:24 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Wed, Dec 10, 2014 at 04:06:56PM +0000, Igor Mammedov wrote:
> > > linker and RSDP tables are build only once, so if later
> > > during rebuild sizes of other ACPI tables change
> > > pointers will be patched incorrectly due to wrong
> > > offsets.
> > > 
> > > To fix it rebuild linker and RSDP tables along with
> > > the rest of ACPI tables so that they would have correct
> > > offsets.
> > > 
> > > Here is a simple reproducer:
> > >  1: hotplug bridge using command:
> > >      device_add pci-bridge,chassis_nr=1
> > >  2: reset system from monitor:
> > >      system_reset
> > > 
> > > As result pointers to ACPI tables are not correct
> > > and guest can't read/parse ACPI tables.
> > > Windows guests just refuse to boot and
> > > Linux guests are more resilient and try to boot without
> > > ACPI, sometimes successfully.
> > > 
> > > PS:
> > >  keep brokenness in 2.2 and older machine types for the sake
> > >  of migration
> > > 
> > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > 
> > I'd like to fix 2.2 as well.
> that's easy,
>  has_imutable_rsdp = true
> should be moved into
>  pc_compat_2_1()
> 
> > 
> > Why does adding bridge in this way cause tables to
> > be resized?
> > I think this is a root-cause that should be fixed.
> That's because there wasn't any bridge described in tables
> on startup, but after hotplug and reset tables are rebuild
> which pickups hotplugged bridge and its secondary PCI bus.
> 
> This behavior seems sane, I'd expect bare-metal behave
> the same way.

For a simple fix, we can skip bridges added by hotplug -
treat them as regular devices.

It defintely seems nicer - at least for old machine types -
than "keep brokenness".

I think the following should do the trcik, but it's completely
untested.
Could you pls try?


diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index b37a397..039776d 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -844,7 +844,8 @@ static void build_pci_bus_end(PCIBus *bus, void *bus_state)
      * Skip bridge subtree creation if bridge hotplug is disabled
      * to make acpi tables compatible with legacy machine types.
      */
-    if (!child->pcihp_bridge_en && bus->parent_dev) {
+    if (bus->parent_dev && (!child->pcihp_bridge_en ||
+                            !DEVICE(bus->parent_dev)->hotplugged)) {
         return;
     }