Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v3 3/3] vhost: Don't call log_access_ok() when using IOTLB
To:     Greg Kurz <groug@kaod.org>, "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,
        qemu-devel@nongnu.org, Laurent Vivier <laurent@vivier.eu>,
        David Gibson <david@gibson.dropbear.id.au>
References: <160171888144.284610.4628526949393013039.stgit@bahia.lan>
 <160171933385.284610.10189082586063280867.stgit@bahia.lan>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <7c512087-639f-0b08-5d8d-6942528d2e06@redhat.com>
Date:   Sat, 10 Oct 2020 11:00:55 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <160171933385.284610.10189082586063280867.stgit@bahia.lan>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk


On 2020/10/3 下午6:02, Greg Kurz wrote:
> When the IOTLB device is enabled, the log_guest_addr that is passed by
> userspace to the VHOST_SET_VRING_ADDR ioctl, and which is then written
> to vq->log_addr, is a GIOVA. All writes to this address are translated
> by log_user() to writes to an HVA, and then ultimately logged through
> the corresponding GPAs in log_write_hva(). No logging will ever occur
> with vq->log_addr in this case. It is thus wrong to pass vq->log_addr
> and log_guest_addr to log_access_vq() which assumes they are actual
> GPAs.
>
> Introduce a new vq_log_used_access_ok() helper that only checks accesses
> to the log for the used structure when there isn't an IOTLB device around.
>
> Signed-off-by: Greg Kurz <groug@kaod.org>


Acked-by: Jason Wang <jasowang@redhat.com>

In the future, we may consider to deprecate log_guest_addr since in any 
case regardless of IOTLB ennoblement we can get GPA from either IOTLB or 
MEM table.

Thanks


> ---
>   drivers/vhost/vhost.c |   23 ++++++++++++++++++-----
>   1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 9d2c225fb518..9ad45e1d27f0 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1370,6 +1370,20 @@ bool vhost_log_access_ok(struct vhost_dev *dev)
>   }
>   EXPORT_SYMBOL_GPL(vhost_log_access_ok);
>   
> +static bool vq_log_used_access_ok(struct vhost_virtqueue *vq,
> +				  void __user *log_base,
> +				  bool log_used,
> +				  u64 log_addr)
> +{
> +	/* If an IOTLB device is present, log_addr is a GIOVA that
> +	 * will never be logged by log_used(). */
> +	if (vq->iotlb)
> +		return true;
> +
> +	return !log_used || log_access_ok(log_base, log_addr,
> +					  vhost_get_used_size(vq, vq->num));
> +}
> +
>   /* Verify access for write logging. */
>   /* Caller should have vq mutex and device mutex */
>   static bool vq_log_access_ok(struct vhost_virtqueue *vq,
> @@ -1377,8 +1391,7 @@ static bool vq_log_access_ok(struct vhost_virtqueue *vq,
>   {
>   	return vq_memory_access_ok(log_base, vq->umem,
>   				   vhost_has_feature(vq, VHOST_F_LOG_ALL)) &&
> -		(!vq->log_used || log_access_ok(log_base, vq->log_addr,
> -				  vhost_get_used_size(vq, vq->num)));
> +		vq_log_used_access_ok(vq, log_base, vq->log_used, vq->log_addr);
>   }
>   
>   /* Can we start vq? */
> @@ -1517,9 +1530,9 @@ static long vhost_vring_set_addr(struct vhost_dev *d,
>   			return -EINVAL;
>   
>   		/* Also validate log access for used ring if enabled. */
> -		if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
> -			!log_access_ok(vq->log_base, a.log_guest_addr,
> -				       vhost_get_used_size(vq, vq->num)))
> +		if (!vq_log_used_access_ok(vq, vq->log_base,
> +				a.flags & (0x1 << VHOST_VRING_F_LOG),
> +				a.log_guest_addr))
>   			return -EINVAL;
>   	}
>   
>
>