On Thu, Mar 20, 2025 at 12:38 AM Dongli Zhang <dongli.zh...@oracle.com> wrote:
>
> Hi Jason,
>
> On 3/17/25 6:12 PM, Jason Wang wrote:
> > On Tue, Mar 18, 2025 at 7:51 AM Dongli Zhang <dongli.zh...@oracle.com>
> > wrote:
> >>
> >> Currently, the only user of vhost_log_write() is vhost-net. The 'len'
> >> argument prevents logging of pages that are not tainted by the RX path.
> >>
> >> Adjustments are needed since more drivers (i.e. vhost-scsi) begin using
> >> vhost_log_write(). So far vhost-net RX path may only partially use pages
> >> shared by the last vring descriptor. Unlike vhost-net, vhost-scsi always
> >> logs all pages shared via vring descriptors. To accommodate this, a new
> >> argument 'partial' is introduced. This argument works alongside 'len' to
> >> indicate whether the driver should log all pages of a vring descriptor, or
> >> only pages that are tainted by the driver.
> >>
> >> In addition, removes BUG().
> >>
> >> Suggested-by: Joao Martins <joao.m.mart...@oracle.com>
> >> Signed-off-by: Dongli Zhang <dongli.zh...@oracle.com>
> >> ---
> >> drivers/vhost/net.c | 2 +-
> >> drivers/vhost/vhost.c | 28 +++++++++++++++++-----------
> >> drivers/vhost/vhost.h | 2 +-
> >> 3 files changed, 19 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> >> index b9b9e9d40951..0e5d82bfde76 100644
> >> --- a/drivers/vhost/net.c
> >> +++ b/drivers/vhost/net.c
> >> @@ -1219,7 +1219,7 @@ 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, true,
> >> vq->iov, in);
> >> total_len += vhost_len;
> >> } while (likely(!vhost_exceeds_weight(vq, ++recv_pkts,
> >> total_len)));
> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >> index 9ac25d08f473..db3b30aba940 100644
> >> --- a/drivers/vhost/vhost.c
> >> +++ b/drivers/vhost/vhost.c
> >> @@ -2304,8 +2304,14 @@ static int log_used(struct vhost_virtqueue *vq, u64
> >> used_offset, u64 len)
> >> return 0;
> >> }
> >>
> >> -int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
> >> - unsigned int log_num, u64 len, struct iovec *iov, int
> >> count)
> >> +/*
> >> + * 'len' is used only when 'partial' is true, to indicate whether the
> >> + * entire length of each descriptor is logged.
> >> + */
> >
> > While at it, let's document all the parameters here.
>
> Sure.
>
> >
> >> +int vhost_log_write(struct vhost_virtqueue *vq,
> >> + struct vhost_log *log, unsigned int log_num,
> >> + u64 len, bool partial,
> >> + struct iovec *iov, int count)
> >> {
> >> int i, r;
> >>
> >> @@ -2323,19 +2329,19 @@ int vhost_log_write(struct vhost_virtqueue *vq,
> >> struct vhost_log *log,
> >> }
> >>
> >> for (i = 0; i < log_num; ++i) {
> >> - u64 l = min(log[i].len, len);
> >> + u64 l = partial ? min(log[i].len, len) : log[i].len;
> >> +
> >> r = log_write(vq->log_base, log[i].addr, l);
> >> if (r < 0)
> >> return r;
> >> - len -= l;
> >> - if (!len) {
> >> - if (vq->log_ctx)
> >> - eventfd_signal(vq->log_ctx);
> >> - return 0;
> >> - }
> >> +
> >> + if (partial)
> >> + len -= l;
> >
> > I wonder if it's simpler to just tweak the caller to call with the
> > correct len (or probably U64_MAX) in this case?
>
> To "tweak the caller to call with the correct len" may need to sum the length
> of all log[i].
>
> Regarding U64_MAX, would you like something below? That is, only use 'len'
> when it isn't U64_MAX.
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 9ac25d08f473..5b49de05e752 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2327,15 +2327,14 @@ int vhost_log_write(struct vhost_virtqueue *vq,
> struct vhost_log *log,
> r = log_write(vq->log_base, log[i].addr, l);
> if (r < 0)
> return r;
> - len -= l;
> - if (!len) {
> - if (vq->log_ctx)
> - eventfd_signal(vq->log_ctx);
> - return 0;
> - }
> +
> + if (len != U64_MAX) ---> It is impossible to have len =
> U64_MAX from vhost-net
> + len -= l; How about keeping those two lines?
> }
> - /* Length written exceeds what we have stored. This is a bug. */
> - BUG();
> +
> + if (vq->log_ctx)
> + eventfd_signal(vq->log_ctx);
> +
> return 0;
> }
> EXPORT_SYMBOL_GPL(vhost_log_write);
Something like this.
Thanks
>
>
> Thank you very much!
>
> Dongli Zhang
>
