On 2021/2/1 下午6:21, Stefano Garzarella wrote:

On Mon, Feb 01, 2021 at 01:40:01PM +0800, Jason Wang wrote:

quoted

On 2021/1/28 下午10:41, Stefano Garzarella wrote:

quoted

__vringh_iov() overwrites the contents of riov and wiov, in fact it
resets the 'i' and 'used' fields, but also the consumed field should
be reset to avoid an inconsistent state.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

I had a question(I remember we had some discussion like this but I 
forget the conclusion):

Sorry, I forgot to update you.

quoted

I see e.g in vringh_getdesc_kern() it has the following comment:

/*
 * Note that you may need to clean up riov and wiov, even on error!
 */

So it looks to me the correct way is to call vringh_kiov_cleanup() 
before?

Looking at the code the right pattern should be:

    vringh_getdesc_*(..., &out_iov, &in_iov, ...);

    // use out_iov and in_iov

    vringh_kiov_cleanup(&out_iov);
    vringh_kiov_cleanup(&in_iov);

This because vringh_getdesc_*() calls __vringh_iov() where 
resize_iovec() is called to allocate the iov wrapped by 'struct 
vringh_kiov' and vringh_kiov_cleanup() frees that memory.

Looking better, __vringh_iov() is able to extend a 'vringh_kiov' 
pre-allocated, so in order to avoid to allocate and free the iov for 
each request we can avoid to call vringh_kiov_cleanup(), but this 
patch is needed to avoid an inconsistent state.

And also patch "vdpa_sim: cleanup kiovs in vdpasim_free()" is required 
to free the iov when the device is going away.

Does that make sense to you?

Make sense.

Maybe I should add a comment in vringh.c to explain this better.

Yes, please.

Thanks

Thanks,
Stefano

quoted

Thanks

quoted

---
 drivers/vhost/vringh.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index f68122705719..bee63d68201a 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c

@@ -290,9 +290,9 @@ __vringh_iov(struct vringh *vrh, u16 i,

         return -EINVAL;
     if (riov)
-        riov->i = riov->used = 0;
+        riov->i = riov->used = riov->consumed = 0;
     if (wiov)
-        wiov->i = wiov->used = 0;
+        wiov->i = wiov->used = wiov->consumed = 0;
     for (;;) {
         void *addr;