On 3/19/2024 8:25 PM, Jason Wang wrote:
On Tue, Mar 19, 2024 at 6:06 AM Si-Wei Liu <si-wei....@oracle.com> wrote:
On 3/17/2024 8:20 PM, Jason Wang wrote:
On Sat, Mar 16, 2024 at 2:33 AM Si-Wei Liu <si-wei....@oracle.com> wrote:
On 3/14/2024 8:50 PM, Jason Wang wrote:
On Fri, Mar 15, 2024 at 5:39 AM Si-Wei Liu <si-wei....@oracle.com> wrote:
There could be a mix of both vhost-user and vhost-kernel clients
in the same QEMU process, where separate vhost loggers for the
specific vhost type have to be used. Make the vhost logger per
backend type, and have them properly reference counted.
It's better to describe what's the advantage of doing this.
Yes, I can add that to the log. Although it's a niche use case, it was
actually a long standing limitation / bug that vhost-user and
vhost-kernel loggers can't co-exist per QEMU process, but today it's
just silent failure that may be ended up with. This bug fix removes that
implicit limitation in the code.
Ok.
Suggested-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Si-Wei Liu <si-wei....@oracle.com>
---
v3->v4:
- remove checking NULL return value from vhost_log_get
v2->v3:
- remove non-effective assertion that never be reached
- do not return NULL from vhost_log_get()
- add neccessary assertions to vhost_log_get()
---
hw/virtio/vhost.c | 45 +++++++++++++++++++++++++++++++++------------
1 file changed, 33 insertions(+), 12 deletions(-)
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 2c9ac79..612f4db 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -43,8 +43,8 @@
do { } while (0)
#endif
-static struct vhost_log *vhost_log;
-static struct vhost_log *vhost_log_shm;
+static struct vhost_log *vhost_log[VHOST_BACKEND_TYPE_MAX];
+static struct vhost_log *vhost_log_shm[VHOST_BACKEND_TYPE_MAX];
/* Memslots used by backends that support private memslots (without an fd).
*/
static unsigned int used_memslots;
@@ -287,6 +287,10 @@ static int vhost_set_backend_type(struct vhost_dev *dev,
r = -1;
}
+ if (r == 0) {
+ assert(dev->vhost_ops->backend_type == backend_type);
+ }
+
Under which condition could we hit this?
Just in case some other function inadvertently corrupted this earlier,
we have to capture discrepancy in the first place... On the other hand,
it will be helpful for other vhost backend writers to diagnose day-one
bug in the code. I feel just code comment here will not be
sufficient/helpful.
See below.
It seems not good to assert a local logic.
It seems to me quite a few local asserts are in the same file already,
vhost_save_backend_state,
For example it has assert for
assert(!dev->started);
which is not the logic of the function itself but require
vhost_dev_start() not to be called before.
But it looks like this patch you assert the code just a few lines
above the assert itself?
Yes, that was the intent - for e.g. xxx_ops may contain corrupted
xxx_ops.backend_type already before coming to this
vhost_set_backend_type() function. And we may capture this corrupted
state by asserting the expected xxx_ops.backend_type (to be consistent
with the backend_type passed in),
This can happen for all variables. Not sure why backend_ops is special.
The assert is just checking the backend_type field only. The other op
fields in backend_ops have similar assert within the op function itself
also. For e.g. vhost_user_requires_shm_log() and a lot of other
vhost_user ops have the following:
assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
vhost_vdpa_vq_get_addr() and a lot of other vhost_vdpa ops have:
assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA);
vhost_kernel ops has similar assertions as well.
The reason why it has to be checked against here is now the callers of
vhost_log_get(), would pass in dev->vhost_ops->backend_type to the API,
which are unable to verify the validity of the backend_type by
themselves. The vhost_log_get() has necessary asserts to make bound
check for the vhost_log[] or vhost_log_shm[] array, but specific assert
against the exact backend type in vhost_set_backend_type() will further
harden the implementation in vhost_log_get() and other backend ops.
which needs be done in the first place
when this discrepancy is detected. In practice I think there should be
no harm to add this assert, but this will add warranted guarantee to the
current code.
For example, such corruption can happen after the assert() so a TOCTOU issue.
Sure, it's best effort only. As pointed out earlier, I think together
with this, there are other similar asserts already in various backend
ops, which could be helpful to nail down the earliest point or a
specific range where things may go wrong in the first place.
Thanks,
-Siwei
Thanks
Regards,
-Siwei
dev->vhost_ops = &xxx_ops;
...
assert(dev->vhost_ops->backend_type == backend_type)
?
Thanks
vhost_load_backend_state,
vhost_virtqueue_mask, vhost_config_mask, just to name a few. Why local
assert a problem?
Thanks,
-Siwei
Thanks
