linux-kernel - Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address

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Message-ID: <15105894-4ec1-1ed0-1976-7b68ed9eeeda@redhat.com>
Date:   Thu, 7 Mar 2019 10:45:57 +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,
        peterx@...hat.com, linux-mm@...ck.org, aarcange@...hat.com
Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel
 virtual address


On 2019/3/7 上午12:31, Michael S. Tsirkin wrote:
>> +static void vhost_set_vmap_dirty(struct vhost_vmap *used)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < used->npages; i++)
>> +		set_page_dirty_lock(used->pages[i]);
> This seems to rely on page lock to mark page dirty.
>
> Could it happen that page writeback will check the
> page, find it clean, and then you mark it dirty and then
> invalidate callback is called?
>
>

Yes. But does this break anything? The page is still there, we just 
remove a kernel mapping to it.

Thanks