linux-kernel - Re: [RFC PATCH V3 0/5] Hi:

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Message-ID: <682d520e-00e3-cdaa-d51e-23524ae48854@redhat.com>
Date:   Tue, 8 Jan 2019 18:12:38 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        davem@...emloft.net
Subject: Re: [RFC PATCH V3 0/5] Hi:


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