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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	davem@davemloft.net
Subject: Re: [RFC PATCH V3 0/5] Hi:
Date: Fri, 11 Jan 2019 16:59:13 +0800	[thread overview]
Message-ID: <303660e9-5ad4-975d-535d-bd158d99884e@redhat.com> (raw)
In-Reply-To: <682d520e-00e3-cdaa-d51e-23524ae48854@redhat.com>


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


      reply	other threads:[~2019-01-11  8:59 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-29 12:46 [RFC PATCH V3 0/5] Hi: Jason Wang
2018-12-29 12:46 ` [RFC PATCH V3 1/5] vhost: generalize adding used elem Jason Wang
2019-01-04 21:29   ` Michael S. Tsirkin
2019-01-05  0:33     ` Sean Christopherson
2019-01-07  7:00       ` Jason Wang
2019-01-07 14:50         ` Michael S. Tsirkin
2018-12-29 12:46 ` [RFC PATCH V3 2/5] vhost: fine grain userspace memory accessors Jason Wang
2018-12-29 12:46 ` [RFC PATCH V3 3/5] vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch() Jason Wang
2018-12-29 12:46 ` [RFC PATCH V3 4/5] vhost: introduce helpers to get the size of metadata area Jason Wang
2018-12-29 12:46 ` [RFC PATCH V3 5/5] vhost: access vq metadata through kernel virtual address Jason Wang
2019-01-04 21:34   ` Michael S. Tsirkin
2019-01-07  8:40     ` Jason Wang
2019-01-02 20:47 ` [RFC PATCH V3 0/5] Hi: Michael S. Tsirkin
2019-01-07  2:19   ` Jason Wang
2019-01-07  3:28     ` Michael S. Tsirkin
2019-01-07  3:53       ` Jason Wang
2019-01-07  4:17         ` Michael S. Tsirkin
2019-01-07  6:50           ` Jason Wang
2019-01-07 14:37             ` Michael S. Tsirkin
2019-01-08 10:01               ` Jason Wang
2019-01-07  7:15           ` Dan Williams
2019-01-07 14:11             ` Michael S. Tsirkin
2019-01-07 21:39               ` Dan Williams
2019-01-07 22:25                 ` Michael S. Tsirkin
2019-01-07 22:44                   ` Dan Williams
2019-01-09  4:31                     ` __get_user slower than get_user (was Re: [RFC PATCH V3 0/5] Hi:) Michael S. Tsirkin
2019-01-09  5:19                       ` Linus Torvalds
2019-01-08 11:42               ` [RFC PATCH V3 0/5] Hi: Jason Wang
2019-01-04 21:41 ` Michael S. Tsirkin
2019-01-07  6:58   ` Jason Wang
2019-01-07 14:47     ` Michael S. Tsirkin
2019-01-08 10:12       ` Jason Wang
2019-01-11  8:59         ` Jason Wang [this message]

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