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);
Thank you very much!
Dongli Zhang
