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

[Jan Kiszka]

On 2013-02-22 04:58, Alexey Korolev wrote:
> 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.

> 
> 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.
> 
> Signed-off-by: Alexey Korolev <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  hw/sysbus.c       |   27 +++++++++++++++++++++++----
>  hw/sysbus.h       |    2 ++
>  target-i386/cpu.c |    3 ++-
>  3 files changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/sysbus.c b/hw/sysbus.c
> index 6d9d1df..50c7232 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 +62,29 @@ 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 {

Coding style: "} 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 dfcf86e..4cf27eb 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2078,7 +2078,8 @@ 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, 0x1000);
                                                  ^^^^^^
Minor, but "0x" makes this look like an address.

>          apic_mapped = 1;
>      }
>  }
> 

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux