Re: [PATCH 0/6] Add various undefined MMIO r/w functions

[Philippe Mathieu-Daudé]

On 6/17/20 3:06 PM, Alex Williamson wrote:
> On Wed, 17 Jun 2020 16:39:56 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
>> On Wed, Jun 17, 2020 at 11:09:27AM +0530, P J P wrote:
>>> From: Prasad J Pandit <pjp@fedoraproject.org>
>>>
>>> Hello,
>>>
>>> This series adds various undefined MMIO read/write functions
>>> to avoid potential guest crash via a NULL pointer dereference.  
>>
>> Hrm.  If this is such a common problem, maybe we should just add a
>> NULL check in the common paths.
> 
> +1, clearly the behavior is already expected.  Thanks,

20 months ago Peter suggested:

"assert that every MemoryRegionOps has pointers to callbacks
 in it, when it is registered in memory_region_init_io() and
 memory_region_init_rom_device_nomigrate()."

https://www.mail-archive.com/qemu-devel@nongnu.org/msg573310.html

Li Qiang refers to this post from Paolo:

>  static const MemoryRegionOps notdirty_mem_ops = {
> +    .read = notdirty_mem_read,
>      .write = notdirty_mem_write,
>      .valid.accepts = notdirty_mem_accepts,
>      .endianness = DEVICE_NATIVE_ENDIAN,

"This cannot happen, since TLB_NOTDIRTY is only added
 to the addr_write member (see accel/tcg/cputlb.c)."

https://www.mail-archive.com/qemu-devel@nongnu.org/msg561345.html