Re: [PATCH net V3] vhost: log dirty page correctly

[Jason Wang]

On 2019/1/15 äå2:04, Michael S. Tsirkin wrote:
> On Fri, Jan 11, 2019 at 12:00:36PM +0800, Jason Wang wrote:
> > Vhost dirty page logging API is designed to sync through GPA. But we
> > try to log GIOVA when device IOTLB is enabled. This is wrong and may
> > lead to missing data after migration.
> >
> > To solve this issue, when logging with device IOTLB enabled, we will:
> >
> > 1) reuse the device IOTLB translation result of GIOVA->HVA mapping to
> >     get HVA, for writable descriptor, get HVA through iovec. For used
> >     ring update, translate its GIOVA to HVA
> > 2) traverse the GPA->HVA mapping to get the possible GPA and log
> >     through GPA. Pay attention this reverse mapping is not guaranteed
> >     to be unique, so we should log each possible GPA in this case.
> >
> > This fix the failure of scp to guest during migration. In -next, we
> > will probably support passing GIOVA->GPA instead of GIOVA->HVA.
> >
> > Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")
> > Reported-by: Jintack Lim<jintack@xxxxxxxxxxxxxxx>
> > Cc: Jintack Lim<jintack@xxxxxxxxxxxxxxx>
> > Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
> > ---
> > Changes from V2:
> > - check and log the case of range overlap
> > - remove unnecessary u64 cast
> > - use smp_wmb() for the case of device IOTLB as well
> > Changes from V1:
> > - return error instead of warn
> > ---
> >   drivers/vhost/net.c   |  3 +-
> >   drivers/vhost/vhost.c | 88 ++++++++++++++++++++++++++++++++++++-------
> >   drivers/vhost/vhost.h |  3 +-
> >   3 files changed, 78 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 36f3d0f49e60..bca86bf7189f 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -1236,7 +1236,8 @@ static void handle_rx(struct vhost_net *net)
> >   		if (nvq->done_idx > VHOST_NET_BATCH)
> >   			vhost_net_signal_used(nvq);
> >   		if (unlikely(vq_log))
> > -			vhost_log_write(vq, vq_log, log, vhost_len);
> > +			vhost_log_write(vq, vq_log, log, vhost_len,
> > +					vq->iov, in);
> >   		total_len += vhost_len;
> >   		if (unlikely(vhost_exceeds_weight(++recv_pkts, total_len))) {
> >   			vhost_poll_queue(&vq->poll);
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 9f7942cbcbb2..55a2e8f9f8ca 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -1733,13 +1733,78 @@ static int log_write(void __user *log_base,
> >   	return r;
> >   }
> >   
> > +static int log_write_hva(struct vhost_virtqueue *vq, u64 hva, u64 len)
> > +{
> > +	struct vhost_umem *umem = vq->umem;
> > +	struct vhost_umem_node *u;
> > +	u64 start, end;
> > +	int r;
> > +	bool hit = false;
> > +
> > +	/* More than one GPAs can be mapped into a single HVA. So
> > +	 * iterate all possible umems here to be safe.
> > +	 */
> > +	list_for_each_entry(u, &umem->umem_list, link) {
> > +		if (u->userspace_addr > hva - 1 + len ||
> > +		    u->userspace_addr - 1 + u->size < hva)
> > +			continue;
> > +		start = max(u->userspace_addr, hva);
> > +		end = min(u->userspace_addr - 1 + u->size, hva - 1 + len);
> > +		r = log_write(vq->log_base,
> > +			      u->start + start - u->userspace_addr,
> > +			      end - start + 1);
> > +		if (r < 0)
> > +			return r;
> > +		hit = true;
> > +	}
> > +
> > +	if (!hit)
> > +		return -EFAULT;
> > +
> > +	return 0;
> > +}
> > +
> I definitely like the simplicity.
>
> But there's one point left here: if len crosses a region boundary,
> but doesn't all fall within a region, we don't consistently report -EFAULT.
>
> So I suspect we need to start by finding a region that contains hva.
> If there are many of these - move right to the end of the
> leftmost one and then repeat until we run out of len
> or fail to find a region and exit with -EFAULT.

Ok, will do it in V4.

Thanks


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