linux-kernel - Re: [PATCH RFC v2 03/10] vringh: reset kiov 'consumed' field in __vringh

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Message-ID: <62bb2e93-4ac3-edf5-2baa-4c2be8257cf0@redhat.com>
Date:   Mon, 1 Feb 2021 13:40:01 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     Xie Yongji <xieyongji@...edance.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Laurent Vivier <lvivier@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        linux-kernel@...r.kernel.org, Max Gurtovoy <mgurtovoy@...dia.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH RFC v2 03/10] vringh: reset kiov 'consumed' field in
 __vringh_iov()


On 2021/1/28 下午10:41, Stefano Garzarella wrote:
> __vringh_iov() overwrites the contents of riov and wiov, in fact it
> resets the 'i' and 'used' fields, but also the consumed field should
> be reset to avoid an inconsistent state.
>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>


I had a question(I remember we had some discussion like this but I 
forget the conclusion):

I see e.g in vringh_getdesc_kern() it has the following comment:

/*
  * Note that you may need to clean up riov and wiov, even on error!
  */

So it looks to me the correct way is to call vringh_kiov_cleanup() before?

Thanks


> ---
>   drivers/vhost/vringh.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index f68122705719..bee63d68201a 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -290,9 +290,9 @@ __vringh_iov(struct vringh *vrh, u16 i,
>   		return -EINVAL;
>   
>   	if (riov)
> -		riov->i = riov->used = 0;
> +		riov->i = riov->used = riov->consumed = 0;
>   	if (wiov)
> -		wiov->i = wiov->used = 0;
> +		wiov->i = wiov->used = wiov->consumed = 0;
>   
>   	for (;;) {
>   		void *addr;