[PATCH v2 04/33] bus/vmbus: fix missing acquire on receive ring index
COOLING9d
REVIEWED: 3 (3M)
From: Stephen Hemminger <stephen@networkplumber.org>
Date: 2026-09-20 18:14:23
Subsystem:
the rest · Maintainer:
Linus Torvalds
1 review trailer.
The receive path checks available data by reading the write index and
then copies ring data. The link between the two is only the comparison,
a control dependency, which does not order load against load on a
weakly ordered architecture: packet data can be read before the host
has finished writing it. Load the write index with acquire, pairing
with the host's release store. This is the equivalent of virt_rmb()
in the Linux hv_pkt_iter code. No change in generated code on x86.
Fixes: 831dba47bd36 ("bus/vmbus: add Hyper-V virtual bus support")
Cc: stable@dpdk.org
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Long Li <longli@microsoft.com>
---
drivers/bus/vmbus/private.h | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/bus/vmbus/private.h b/drivers/bus/vmbus/private.h
index 6efac86b77..aca5b534f9 100644
--- a/drivers/bus/vmbus/private.h
+++ b/drivers/bus/vmbus/private.h@@ -12,6 +12,7 @@ #include <bus_driver.h> #include <bus_vmbus_driver.h> #include <rte_log.h> +#include <rte_stdatomic.h> #include <rte_eal_paging.h> #include <rte_vmbus_reg.h>
@@ -130,7 +131,16 @@ vmbus_br_availwrite(const struct vmbus_br *br, uint32_t windex) static inline uint32_t vmbus_br_availread(const struct vmbus_br *br) { - return br->dsize - vmbus_br_availwrite(br, br->vbr->windex); + uint32_t windex; + + /* Pairs with the host's release store of the write index; + * ring data must not be read before the index. + */ + windex = rte_atomic_load_explicit( + (volatile uint32_t __rte_atomic *)&br->vbr->windex, + rte_memory_order_acquire); + + return br->dsize - vmbus_br_availwrite(br, windex); } int vmbus_txbr_write(struct vmbus_br *tbr, const struct iovec iov[], int iovlen,
--
2.53.0