Re: [RFC PATCH V3 0/5] Hi:

Jason Wang
2019-01-11T08:59:13Z

On 2019/1/8 下午6:12, Jason Wang wrote:
>
> On 2019/1/7 下午10:47, Michael S. Tsirkin wrote:
>> On Mon, Jan 07, 2019 at 02:58:08PM +0800, Jason Wang wrote:
>>> On 2019/1/5 上午5:41, Michael S. Tsirkin wrote:
>>>> On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:
>>>>> This series tries to access virtqueue metadata through kernel virtual
>>>>> address instead of copy_user() friends since they had too much
>>>>> overheads like checks, spec barriers or even hardware feature
>>>>> toggling.
>>>> I think it's a reasonable approach.
>>>> However I need to look at whether and which mmu notifiers are
>>>> invoked before
>>>> writeback. Do you know?
>>>
>>> I don't know but just looking at the MMU notifier ops definition,
>>> there's no
>>> such callback if my understanding is correct.
>>>
>>> Thanks
>> In that case how are you making sure used ring updates are written back?
>> If they aren't guest will crash ...
>
>
> I think this is the writeback issue you mentioned early. I don't do a
> followup on the pointer but it looks to me some work is ongoing to fix
> the issue.
>
> I can investigate it more, but it's not something new, consider the
> case of VFIO.
>
> Thanks

Ok, after some investigation. The GUP + dirty pages issue is not easy to
be fixed so it may still take a while.

An idea is switch back to copy_user() friends if we find the metadata
page is not anonymous.

Does this sound good to you?

Thanks