Re: [Qemu-devel] [PATCH] exec: don't return int64_t in address_space_cache_init()

[Jason Wang <jasowang@redhat.com>]

On 2017年03月30日 05:26, Michael S. Tsirkin wrote:
> On Wed, Mar 29, 2017 at 02:12:50PM +0800, Jason Wang wrote:
>> We return int64_t as the length of region cache but accept hwaddr as
>> the required length. This is wrong and may confuse the caller since
>> the it can lead comparison between signed and unsigned types. The
>> caller can not catch the failure in this case. Fixing this by
>> returning hwaddr and return zero on failure.
>>
>> Fixes: 5eba0404b9829 ("virtio: use MemoryRegionCache to access descriptors")
>> Fixes: e45da65322386 ("virtio: validate address space cache during init")
>> Cc: Cornelia Huck<cornelia.huck@de.ibm.com>
>> Cc: Paolo Bonzini<pbonzini@redhat.com>
>> Signed-off-by: Jason Wang<jasowang@redhat.com>
> Can you be more specific about the symptoms this fixes in the
> commit log?
> E.g. "This actually triggers on XYZ when using ABC".
>
>

I want do this, but in fact this was triggered by a bug of qemu (see the 
thread of iommu reset vs region cache).

In that case, when used map fails, then check

      if (len < size) {
         virtio_error(vdev, "Cannot map used");
         goto err_used;
     }

can not catch the -EFAULT, since len is converted to unsigned.

Thanks