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    SubjectRe: [PATCH v2 1/2] vhost: fix vhost_vq_access_ok() log check
    On Tue, Apr 10, 2018 at 04:22:35PM +0300, Michael S. Tsirkin wrote:
    > On Tue, Apr 10, 2018 at 01:26:29PM +0800, Stefan Hajnoczi wrote:
    > > Commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ("vhost: validate log
    > > when IOTLB is enabled") introduced a regression. The logic was
    > > originally:
    > >
    > > if (vq->iotlb)
    > > return 1;
    > > return A && B;
    > >
    > > After the patch the short-circuit logic for A was inverted:
    > >
    > > if (A || vq->iotlb)
    > > return A;
    > > return B;
    > >
    > > This patch fixes the regression by rewriting the checks in the obvious
    > > way, no longer returning A when vq->iotlb is non-NULL (which is hard to
    > > understand).
    > >
    > > Reported-by: syzbot+65a84dde0214b0387ccd@syzkaller.appspotmail.com
    > > Cc: Jason Wang <jasowang@redhat.com>
    > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
    >
    > This patch only makes sense after patch 2/2 is applied.
    > Otherwise the logic seems reversed below.
    >
    > Can you pls squash these two?

    Oh, in fact the patch is ok. This just goes to show
    that patch 2/2 is useful. But squashing is not required.
    Sorry about the noise.

    Acked-by: Michael S. Tsirkin <mst@redhat.com>
    Fixes: d65026c6c ("vhost: validate log when IOTLB is enabled")

    probably stable material since patch it fixes was queued to stable?


    > > ---
    > > drivers/vhost/vhost.c | 8 +++++---
    > > 1 file changed, 5 insertions(+), 3 deletions(-)
    > >
    > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
    > > index 5320039671b7..93fd0c75b0d8 100644
    > > --- a/drivers/vhost/vhost.c
    > > +++ b/drivers/vhost/vhost.c
    > > @@ -1244,10 +1244,12 @@ static int vq_log_access_ok(struct vhost_virtqueue *vq,
    > > /* Caller should have vq mutex and device mutex */
    > > int vhost_vq_access_ok(struct vhost_virtqueue *vq)
    > > {
    > > - int ret = vq_log_access_ok(vq, vq->log_base);
    > > + if (!vq_log_access_ok(vq, vq->log_base))
    > > + return 0;
    > >
    > > - if (ret || vq->iotlb)
    > > - return ret;
    > > + /* Access validation occurs at prefetch time with IOTLB */
    > > + if (vq->iotlb)
    > > + return 1;
    > >
    > > return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
    > > }
    > > --
    > > 2.14.3

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