Re: [Qemu-devel] [PATCH 2/5] pvrdma: add uar_read routine

[李强]

At 2018-12-11 23:22:32, "Yuval Shaia" <address@hidden> wrote:
>On Tue, Dec 11, 2018 at 06:56:39PM +0530, P J P wrote:
>> From: Prasad J Pandit <address@hidden>
>> 
>> Define skeleton 'uar_read' routine. Avoid NULL dereference.
>> 
>> Reported-by: Li Qiang <address@hidden>
>> Signed-off-by: Prasad J Pandit <address@hidden>
>> ---
>>  hw/rdma/vmw/pvrdma_main.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/hw/rdma/vmw/pvrdma_main.c b/hw/rdma/vmw/pvrdma_main.c
>> index ca5fa8d981..a6211d416d 100644
>> --- a/hw/rdma/vmw/pvrdma_main.c
>> +++ b/hw/rdma/vmw/pvrdma_main.c
>> @@ -455,6 +455,11 @@ static const MemoryRegionOps regs_ops = {
>>      },
>>  };
>>  
>> +static uint64_t uar_read(void *opaque, hwaddr addr, unsigned size)
>> +{
>> +    return 0;
>> +}
>> +
>>  static void uar_write(void *opaque, hwaddr addr, uint64_t val, unsigned 
>> size)
>>  {
>>      PVRDMADev *dev = opaque;
>> @@ -496,6 +501,7 @@ static void uar_write(void *opaque, hwaddr addr, 
>> uint64_t val, unsigned size)
>>  }
>>  
>>  static const MemoryRegionOps uar_ops = {
>> +    .read = uar_read,
>

>Are you sure it is needed?


I'm quite sure this.
The issue here is that in memory_region_dispatch_read1
if there is no mr's read callback, the 'memory_region_read_with_attrs_accessor' 
will be called, but in that the 'mr->ops->raed_with_attrs' has no check.


In fact, I have send out a patch for the framework:
-->https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg02265.html


But no more response.


>Looking at memory_region_dispatch_read1 i can see that there is a check but 
>>not sure this is the right place. Anyways, if it is not, i believe this
>should be framework responsibility.


Reference Peter's answer here:
-->https://lists.gnu.org/archive/html/qemu-devel/2018-09/msg01404.html


"Currently our semantics are "you must provide both read and write, even
if one of them just always returns 0 / does nothing / returns an error".
We could probably reasonably assert this at the point when the
MemoryRegionOps is registered."




Thanks,
Li Qiang


> >> .write = uar_write, >> .endianness = DEVICE_LITTLE_ENDIAN, >> .impl = { >> 
> >> -- >> 2.19.2 >>