Re: [Xen-devel] [PATCH for-2.10 v2 1/2] hw/acpi: Call acpi_set_pci_info when no ACPI tables needed

[Igor Mammedov <imammedo@xxxxxxxxxx>]

On Tue, 15 Aug 2017 22:24:08 +0300
"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:

> On Tue, Aug 15, 2017 at 02:07:51PM +0200, Igor Mammedov wrote:
> > On Tue, 15 Aug 2017 12:15:48 +0100
> > Anthony PERARD <anthony.perard@xxxxxxxxxx> wrote:
> >   
> > > To do PCI passthrough with Xen, the property acpi-pcihp-bsel needs to be
> > > set, but this was done only when ACPI tables are built which is not
> > > needed for a Xen guest. The need for the property starts with commit
> > > "pc: pcihp: avoid adding ACPI_PCIHP_PROP_BSEL twice"
> > > (f0c9d64a68b776374ec4732424a3e27753ce37b6).
> > > 
> > > Set pci info before checking for the needs to build ACPI tables.
> > > 
> > > Assign bsel=0 property only to the root bus on Xen as there is no
> > > support in the Xen ACPI tables for a different value.  
> > 
> > looking at hw/acpi/pcihp.c and bsel usage there it looks like
> > bsel property is owned by it and not by ACPI tables, so instead of
> > shuffling it in acpi_setup(), how about moving bsel initialization
> > to hw/acpi/pcihp.c and initialize it there unconditionally?
> > 
> > It could be as simple as moving acpi_set_pci_info()/acpi_set_bsel()
> > there and calling it from acpi_pcihp_reset().
> > 
> > Then there won't be need for Xen specific branches, as root bus
> > will have bsel set automatically which is sufficient for Xen and
> > the rest of bsel-s (bridges) will be just unused by Xen,
> > which could later extend its ACPI table implementation to utilize them.   
> 
> Later is exactly what I'd like to try to avoid.
> Whoever wants acpi hotplug for bridges needs to get
> the bsel info from qemu supplied acpi tables.

I'd prefer to have only one behavior in QEMU (on hw interface)
side and let Xen to maintain their own ACPI tables  dealing
with issues that arise from it since they insist on doing job twice.

The point is bsel is so embedded in HW part of impl.
that it should be allocated/manged there, otherwise it leads
to hacks where acpi_setup() is called but does partial init
and then bails out to fix code pcihp.c that depend on it being run,
pcihp.c (hw part) shouldn't depend on on ACPI tables generation
(bios part).

Anyway if you insist on capping Xen, it probably could be done
with comat machinery, something like this:

(where the 1st hunk should been there since, we've introduced
"acpi-pci-hotplug-with-bridge-support")

diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
index c420a38..a55f022 100644
--- a/hw/acpi/pcihp.c
+++ b/hw/acpi/pcihp.c
@@ -273,7 +273,7 @@ static void pci_write(void *opaque, hwaddr addr, uint64_t 
data,
                       addr, data);
         break;
     case PCI_SEL_BASE:
-        s->hotplug_select = data;
+        s->hotplug_select = s->legacy_piix ? 0 : data;
         ACPI_PCIHP_DPRINTF("pcisel write %" HWADDR_PRIx " <== %" PRIu64 "\n",
                       addr, data);
     default:
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 22dbef6..81b8c3e 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -1117,6 +1117,13 @@ static void xenfv_machine_options(MachineClass *m)
     m->max_cpus = HVM_MAX_VCPUS;
     m->default_machine_opts = "accel=xen";
     m->hot_add_cpu = pc_hot_add_cpu;
+    SET_MACHINE_COMPAT(m,
+        {\
+            .driver   = "PIIX4_PM",\
+            .property = "acpi-pci-hotplug-with-bridge-support",\
+            .value    = "off",\
+        },
+    );
 }
 
 DEFINE_PC_MACHINE(xenfv, "xenfv", pc_xen_hvm_init,



> > > Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> > > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> > > 
> > > ---
> > > Changes in V2:
> > >   - check for acpi_enabled before calling acpi_set_pci_info.
> > >   - set the property on the root bus only.
> > > 
> > > This patch would be a canditade to backport to 2.9.
> > > 
> > > CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > CC: Bruce Rogers <brogers@xxxxxxxx>
> > > ---
> > >  hw/i386/acpi-build.c | 25 ++++++++++++++++---------
> > >  1 file changed, 16 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > > index 98dd424678..c0483b96cf 100644
> > > --- a/hw/i386/acpi-build.c
> > > +++ b/hw/i386/acpi-build.c
> > > @@ -46,6 +46,7 @@
> > >  #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"
> > > @@ -518,8 +519,13 @@ static void acpi_set_pci_info(void)
> > >      unsigned bsel_alloc = ACPI_PCIHP_BSEL_DEFAULT;
> > >  
> > >      if (bus) {
> > > -        /* Scan all PCI buses. Set property to enable acpi based 
> > > hotplug. */
> > > -        pci_for_each_bus_depth_first(bus, acpi_set_bsel, NULL, 
> > > &bsel_alloc);
> > > +        if (xen_enabled()) {
> > > +            /* Assign BSEL property to root bus only. */
> > > +            acpi_set_bsel(bus, &bsel_alloc);
> > > +        } else {
> > > +            /* Scan all PCI buses. Set property to enable acpi based 
> > > hotplug. */
> > > +            pci_for_each_bus_depth_first(bus, acpi_set_bsel, NULL, 
> > > &bsel_alloc);
> > > +        }
> > >      }
> > >  }
> > >  
> > > @@ -2871,6 +2877,14 @@ void acpi_setup(void)
> > >      AcpiBuildState *build_state;
> > >      Object *vmgenid_dev;
> > >  
> > > +    if (!acpi_enabled) {
> > > +        ACPI_BUILD_DPRINTF("ACPI disabled. Bailing out.\n");
> > > +        return;
> > > +    }
> > > +
> > > +    /* Assign BSEL property on hotpluggable PCI buses. */
> > > +    acpi_set_pci_info();
> > > +
> > >      if (!pcms->fw_cfg) {
> > >          ACPI_BUILD_DPRINTF("No fw cfg. Bailing out.\n");
> > >          return;
> > > @@ -2881,15 +2895,8 @@ void acpi_setup(void)
> > >          return;
> > >      }
> > >  
> > > -    if (!acpi_enabled) {
> > > -        ACPI_BUILD_DPRINTF("ACPI disabled. Bailing out.\n");
> > > -        return;
> > > -    }
> > > -
> > >      build_state = g_malloc0(sizeof *build_state);
> > >  
> > > -    acpi_set_pci_info();
> > > -
> > >      acpi_build_tables_init(&tables);
> > >      acpi_build(&tables, MACHINE(pcms));
> > >    


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