Re: [PATCH net V2] vhost: log dirty page correctly

[Jason Wang]

On 2019/1/10 äå10:07, Michael S. Tsirkin wrote:
> On Thu, Jan 10, 2019 at 08:37:17PM +0800, Jason Wang wrote:
> > On 2019/1/9 äå10:25, Michael S. Tsirkin wrote:
> > > On Wed, Jan 09, 2019 at 03:29:47PM +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>
> > > > ---
> > > > The patch is needed for stable.
> > > > Changes from V1:
> > > > - return error instead of warn
> > > > ---
> > > >    drivers/vhost/net.c   |  3 +-
> > > >    drivers/vhost/vhost.c | 82 +++++++++++++++++++++++++++++++++++--------
> > > >    drivers/vhost/vhost.h |  3 +-
> > > >    3 files changed, 72 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..ee095f08ffd4 100644
> > > > --- a/drivers/vhost/vhost.c
> > > > +++ b/drivers/vhost/vhost.c
> > > > @@ -1733,11 +1733,70 @@ 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 gpa;
> > > > +	int r;
> > > > +	bool hit = false;
> > > > +
> > > > +	list_for_each_entry(u, &umem->umem_list, link) {
> > > > +		if (u->userspace_addr < hva &&
> > > > +		    u->userspace_addr + u->size >=
> > > > +		    hva + len) {
> > > So this tries to see that the GPA range is completely within
> > > the GVA region. Does this have to be the case?
> > You mean e.g a buffer that crosses the boundary of two memory regions?
> Yes - where hva and gva could be contigious.


Ok, let me add the overlap range logging in v3.


> > > And if yes why not return 0 below instead of hit = true?
> > I think it's safe but not sure for the case like two GPAs can map to same
> > HVA?
> Oh I see. Yes that's possible. Document the motivation?

Ok.

Thanks