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Date: Mon, 14 Jan 2019 13:04:45 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Jintack Lim <jintack@...columbia.edu>
Subject: Re: [PATCH net V3] vhost: log dirty page correctly
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@...columbia.edu>
> Cc: Jintack Lim <jintack@...columbia.edu>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> 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.
> +static int log_used(struct vhost_virtqueue *vq, u64 used_offset, u64 len)
> +{
> + struct iovec iov[64];
> + int i, ret;
> +
> + if (!vq->iotlb)
> + return log_write(vq->log_base, vq->log_addr + used_offset, len);
> +
> + ret = translate_desc(vq, (uintptr_t)vq->used + used_offset,
> + len, iov, 64, VHOST_ACCESS_WO);
> + if (ret)
> + return ret;
> +
> + for (i = 0; i < ret; i++) {
> + ret = log_write_hva(vq, (uintptr_t)iov[i].iov_base,
> + iov[i].iov_len);
> + if (ret)
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
> - unsigned int log_num, u64 len)
> + unsigned int log_num, u64 len, struct iovec *iov, int count)
> {
> int i, r;
>
> /* Make sure data written is seen before log. */
> smp_wmb();
> +
> + if (vq->iotlb) {
> + for (i = 0; i < count; i++) {
> + r = log_write_hva(vq, (uintptr_t)iov[i].iov_base,
> + iov[i].iov_len);
> + if (r < 0)
> + return r;
> + }
> + return 0;
> + }
> +
> for (i = 0; i < log_num; ++i) {
> u64 l = min(log[i].len, len);
> r = log_write(vq->log_base, log[i].addr, l);
> @@ -1769,9 +1834,8 @@ static int vhost_update_used_flags(struct vhost_virtqueue *vq)
> smp_wmb();
> /* Log used flag write. */
> used = &vq->used->flags;
> - log_write(vq->log_base, vq->log_addr +
> - (used - (void __user *)vq->used),
> - sizeof vq->used->flags);
> + log_used(vq, (used - (void __user *)vq->used),
> + sizeof vq->used->flags);
> if (vq->log_ctx)
> eventfd_signal(vq->log_ctx, 1);
> }
> @@ -1789,9 +1853,8 @@ static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
> smp_wmb();
> /* Log avail event write */
> used = vhost_avail_event(vq);
> - log_write(vq->log_base, vq->log_addr +
> - (used - (void __user *)vq->used),
> - sizeof *vhost_avail_event(vq));
> + log_used(vq, (used - (void __user *)vq->used),
> + sizeof *vhost_avail_event(vq));
> if (vq->log_ctx)
> eventfd_signal(vq->log_ctx, 1);
> }
> @@ -2191,10 +2254,8 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
> /* Make sure data is seen before log. */
> smp_wmb();
> /* Log used ring entry write. */
> - log_write(vq->log_base,
> - vq->log_addr +
> - ((void __user *)used - (void __user *)vq->used),
> - count * sizeof *used);
> + log_used(vq, ((void __user *)used - (void __user *)vq->used),
> + count * sizeof *used);
> }
> old = vq->last_used_idx;
> new = (vq->last_used_idx += count);
> @@ -2236,9 +2297,8 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
> /* Make sure used idx is seen before log. */
> smp_wmb();
> /* Log used index update. */
> - log_write(vq->log_base,
> - vq->log_addr + offsetof(struct vring_used, idx),
> - sizeof vq->used->idx);
> + log_used(vq, offsetof(struct vring_used, idx),
> + sizeof vq->used->idx);
> if (vq->log_ctx)
> eventfd_signal(vq->log_ctx, 1);
> }
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 466ef7542291..1b675dad5e05 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -205,7 +205,8 @@ bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
> bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
>
> int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
> - unsigned int log_num, u64 len);
> + unsigned int log_num, u64 len,
> + struct iovec *iov, int count);
> int vq_iotlb_prefetch(struct vhost_virtqueue *vq);
>
> struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type);
> --
> 2.17.1
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