Drivers: hv: vmbus: Compute ring byte counts from a caller-held snapshot

hv_get_ringbuffer_availbytes() reads the indices directly, so a caller
that also wants the index values has to read them a second time. The
host can change them in between, resulting in the byte counts and the
indices reflecting two different states of the ring.

Replace it with hv_ringbuffer_avail_write() and
hv_ringbuffer_avail_read(), which take the indices as arguments and
return a single count. They are separate because most callers want only
one of the two values. Use them in hv_ringbuffer_write() in place of the
open-coded equivalent. hv_get_bytes_to_read(), hv_get_bytes_to_write()
and hv_pkt_iter_avail() duplicated the same arithmetic, so put the
helpers in include/linux/hyperv.h and use them there too.

Add a hv_ringbuffer_indices_invalid() helper that bounds checks a pair
of read and write indices, and use it for the check in
hv_ringbuffer_write(). Convert the remaining callers to use a single
snapshot:

  - hv_ringbuffer_get_debuginfo() now reports the indices and the
    computed byte counts from the same snapshot.

  - hv_pkt_iter_close() computes the free space from priv_read_index
    instead of re-reading the shared read index. The two agree unless a
    misbehaving host has rewritten the value.

No functional change intended for a well-behaved host.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

0 files changed, 0 insertions, 0 deletions