Re: [Qemu-devel] [PATCH] amd_iommu: Return error on machines with no PCI

[Thomas Huth <thuth@redhat.com>]

On 14.09.2017 22:18, Mohammed Gamal wrote:
> Starting the following command line causes a segfault
> qemu-system-x86_64 -S -machine isapc,accel=kvm -device amd-iommu
> 
> This is due to the fact that the machine type 'isapc' doesn't have
> a PCI bus, while amd_iommu doesn't check if the machine has PCI support
> and subsequently does a null-pointer access. AMD IOMMU shouldn't even work
> if the target machine doesn't have PCI.
> 
> Add a check for PCI on the given machine type and return an error if PCI
> is not supported.
> 
> Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> ---
>  hw/i386/amd_iommu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> index 334938a..9a667b7 100644
> --- a/hw/i386/amd_iommu.c
> +++ b/hw/i386/amd_iommu.c
> @@ -1153,6 +1153,13 @@ static void amdvi_realize(DeviceState *dev, Error **err)
>      }
>  
>      bus = pcms->bus;
> +
> +    if (!bus) {
> +        error_setg(err, "Machine-type '%s' does not support PCI",
> +                   mc->name);
> +        return;
> +    }
> +
>      s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
>                                       amdvi_uint64_equal, g_free, g_free);
>  
> 

Patch looks fine to me, but I think it would also be sufficient to
change the check at the beginning of the function to test "if (!pcms ||
!pcms->bus)" instead of just "if (!pcms)" ... the error message
"Machine-type 'xxx' not supported by amd-iommu" is also adequate if
there is no PCI bus available on the system.

 Thomas