Re: [Qemu-devel] [PATCH v2] Fix guest OS hang when 64bit PCI bar present

[Alexey Korolev]

>> This patch addresses the issue fully described here:
>> http://lists.nongnu.org/archive/html/qemu-devel/2013-02/msg01804.html
>> 
>> Linux kernels prior to 2.6.36 do not disable the PCI device during
>> enumeration process. Since lower and higher parts of a 64bit BAR
>> are programmed separately this leads to qemu receiving a request to occupy
>> a completely wrong address region for a short period of time.
>> We have found that the boot process screws up completely if kvm-apic range
>> is overlapped even for a short period of time (it is fine for other
>> regions though).
> 
> So the issue it that we hide the MSI target region from the device
> models for a "short periods of time"? How short is this? It would be
>good to fully understand what goes "completely wrong" to avoid that we
> miss to fix something else (IO-APIC, HPET) or even paper over a problem
> of the memory subsystem.
As far as I can understand the region corruption and recovery happens within
one call of pci_read_bases of linux kernel enumeration:
(http://lxr.linux.no/#linux+v2.6.21/drivers/pci/probe.c#L173)
Unfortunately I cannot even guess what is happening with kvm-apic-msi, or why
it does not tolerate overlaps. This is actually a still open qestion.

>> 
>> This patch raises the priority of the kvm-apic memory region, so it is
>> never pushed out by PCI devices. The patch is quite safe as it does not
>> touch memory manager.

I have fixed styling issues. Please use this version.

Signed-off-by: Alexey Korolev <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 hw/sysbus.c       |   26 ++++++++++++++++++++++----
 hw/sysbus.h       |    2 ++
 target-i386/cpu.c |    3 ++-
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/hw/sysbus.c b/hw/sysbus.c
index 6d9d1df..242eb1e 100644
--- a/hw/sysbus.c
+++ b/hw/sysbus.c
@@ -48,7 +48,8 @@ void sysbus_connect_irq(SysBusDevice *dev, int n, qemu_irq 
irq)
     }
 }
 
-void sysbus_mmio_map(SysBusDevice *dev, int n, hwaddr addr)
+static void sysbus_mmio_map_common(SysBusDevice *dev, int n, hwaddr addr,
+                                   bool may_overlap, unsigned priority)
 {
     assert(n >= 0 && n < dev->num_mmio);
 
@@ -61,11 +62,28 @@ void sysbus_mmio_map(SysBusDevice *dev, int n, hwaddr addr)
         memory_region_del_subregion(get_system_memory(), dev->mmio[n].memory);
     }
     dev->mmio[n].addr = addr;
-    memory_region_add_subregion(get_system_memory(),
-                                addr,
-                                dev->mmio[n].memory);
+    if (may_overlap) {
+        memory_region_add_subregion_overlap(get_system_memory(),
+                                            addr,
+                                            dev->mmio[n].memory,
+                                            priority);
+    } else {
+        memory_region_add_subregion(get_system_memory(),
+                                    addr,
+                                    dev->mmio[n].memory);
+    }
+}
+
+void sysbus_mmio_map(SysBusDevice *dev, int n, hwaddr addr)
+{
+    sysbus_mmio_map_common(dev, n, addr, false, 0);
 }
 
+void sysbus_mmio_map_overlap(SysBusDevice *dev, int n, hwaddr addr,
+                             unsigned priority)
+{
+    sysbus_mmio_map_common(dev, n, addr, true, priority);
+}
 
 /* Request an IRQ source.  The actual IRQ object may be populated later.  */
 void sysbus_init_irq(SysBusDevice *dev, qemu_irq *p)
diff --git a/hw/sysbus.h b/hw/sysbus.h
index a7fcded..2100bd7 100644
--- a/hw/sysbus.h
+++ b/hw/sysbus.h
@@ -56,6 +56,8 @@ void sysbus_init_ioports(SysBusDevice *dev, pio_addr_t 
ioport, pio_addr_t size);
 
 void sysbus_connect_irq(SysBusDevice *dev, int n, qemu_irq irq);
 void sysbus_mmio_map(SysBusDevice *dev, int n, hwaddr addr);
+void sysbus_mmio_map_overlap(SysBusDevice *dev, int n, hwaddr addr,
+                             unsigned priority);
 void sysbus_add_memory(SysBusDevice *dev, hwaddr addr,
                        MemoryRegion *mem);
 void sysbus_add_memory_overlap(SysBusDevice *dev, hwaddr addr,
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 5582e5f..4b72094 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2088,7 +2088,8 @@ static void x86_cpu_apic_init(X86CPU *cpu, Error **errp)
         /* NOTE: the APIC is directly connected to the CPU - it is not
            on the global memory bus. */
         /* XXX: what if the base changes? */
-        sysbus_mmio_map(SYS_BUS_DEVICE(env->apic_state), 0, MSI_ADDR_BASE);
+        sysbus_mmio_map_overlap(SYS_BUS_DEVICE(env->apic_state), 0,
+                                MSI_ADDR_BASE, 1000);
         apic_mapped = 1;
     }
 }
-- 
1.7.9.5