Re: [Qemu-devel] [PATCH qemu] pci: Only unmap bus_master_enabled_region if was added previously

[Max Reitz]

On 31.03.2017 06:47, Alexey Kardashevskiy wrote:
> Normally pci_init_bus_master() would be called either via
> bus->machine_done.notify or directly from do_pci_register_device().
> 
> However if a device's realize() failed, pci_init_bus_master() is not
> called, and do_pci_unregister_device() fails on
> memory_region_del_subregion() as it was not mapped.
> 
> This adds a check that subregion was mapped before unmapping it.
> 
> Fixes: c53598ed18e4 ("pci: Add missing drop of bus master AS reference")
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> ---
> This is to pass iotest 051 which does run QEMU like this:
> 
> ppc64-softmmu/qemu-system-ppc64 -nodefaults -machine accel=qtest -nographic 
> -monitor stdio -serial none -drive if=virtio
> 
> which normally fails with:
> 
> qemu-system-ppc64: -drive if=virtio: Device needs media, but drive is empty
> 
> or asserts (without this patch):
> 
> qemu-system-ppc64: /home/aik/p/qemu-kvm/memory.c:2118: 
> memory_region_del_subregion: Assertion `subregion->container == mr' failed.
> ---
>  hw/pci/pci.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index bd8043c460..259483b1c0 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -869,8 +869,10 @@ static void do_pci_unregister_device(PCIDevice *pci_dev)
>      pci_dev->bus->devices[pci_dev->devfn] = NULL;
>      pci_config_free(pci_dev);
>  
> -    memory_region_del_subregion(&pci_dev->bus_master_container_region,
> -                                &pci_dev->bus_master_enable_region);
> +    if (memory_region_is_mapped(&pci_dev->bus_master_enable_region)) {
> +        memory_region_del_subregion(&pci_dev->bus_master_container_region,
> +                                    &pci_dev->bus_master_enable_region);
> +    }
>      address_space_destroy(&pci_dev->bus_master_as);
>  }

I'm not sure whether it's generally assumed to be safe to call
memory_region_is_mapped() on "uninitialized" memory regions
(bus_master_enable_region is just completely zeroed out before
pci_init_bus_master(), as far as I can see and guess), but it certainly
works in practice, so:

Reviewed-by: Max Reitz <address@hidden>

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