[PATCH net 2/5] hv_netvsc: Use vmbus_sendpacket_mpb_desc() to send VMBus messages

mhkelley58
2025-05-13T00:06:23Z

From: Michael Kelley <mhklinux@outlook.com>

netvsc currently uses vmbus_sendpacket_pagebuffer() to send VMBus
messages. This function creates a series of GPA ranges, each of which
contains a single PFN. However, if the rndis header in the VMBus
message crosses a page boundary, the netvsc protocol with the host
requires that both PFNs for the rndis header must be in a single "GPA
range" data structure, which isn't possible with
vmbus_sendpacket_pagebuffer(). As the first step in fixing this, add a
new function netvsc_build_mpb_array() to build a VMBus message with
multiple GPA ranges, each of which may contain multiple PFNs. Use
vmbus_sendpacket_mpb_desc() to send this VMBus message to the host.

There's no functional change since higher levels of netvsc don't
maintain or propagate knowledge of contiguous PFNs. Based on its
input, netvsc_build_mpb_array() still produces a separate GPA range
for each PFN and the behavior is the same as with
vmbus_sendpacket_pagebuffer(). But the groundwork is laid for a
subsequent patch to provide the necessary grouping.

Cc: <stable@vger.kernel.org> # 6.1.x
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
---
drivers/net/hyperv/netvsc.c | 50 +++++++++++++++++++++++++++++++++----
1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index d6f5b9ea3109..6d1705f87682 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1055,6 +1055,42 @@ static int netvsc_dma_map(struct hv_device *hv_dev,
return 0;
}

+/* Build an "array" of mpb entries describing the data to be transferred
+ * over VMBus. After the desc header fields, each "array" entry is variable
+ * size, and each entry starts after the end of the previous entry. The
+ * "offset" and "len" fields for each entry imply the size of the entry.
+ *
+ * The pfns are in HV_HYP_PAGE_SIZE, because all communication with Hyper-V
+ * uses that granularity, even if the system page size of the guest is larger.
+ * Each entry in the input "pb" array must describe a contiguous range of
+ * guest physical memory so that the pfns are sequential if the range crosses
+ * a page boundary. The offset field must be < HV_HYP_PAGE_SIZE.
+ */
+static inline void netvsc_build_mpb_array(struct hv_page_buffer *pb,
+ u32 page_buffer_count,
+ struct vmbus_packet_mpb_array *desc,
+ u32 *desc_size)
+{
+ struct hv_mpb_array *mpb_entry = &desc->range;
+ int i, j;
+
+ for (i = 0; i < page_buffer_count; i++) {
+ u32 offset = pb[i].offset;
+ u32 len = pb[i].len;
+
+ mpb_entry->offset = offset;
+ mpb_entry->len = len;
+
+ for (j = 0; j < HVPFN_UP(offset + len); j++)
+ mpb_entry->pfn_array[j] = pb[i].pfn + j;
+
+ mpb_entry = (struct hv_mpb_array *)&mpb_entry->pfn_array[j];
+ }
+
+ desc->rangecount = page_buffer_count;
+ *desc_size = (char *)mpb_entry - (char *)desc;
+}
+
static inline int netvsc_send_pkt(
struct hv_device *device,
struct hv_netvsc_packet *packet,
@@ -1097,6 +1133,9 @@ static inline int netvsc_send_pkt(

packet->dma_range = NULL;
if (packet->page_buf_cnt) {
+ struct vmbus_channel_packet_page_buffer desc;
+ u32 desc_size;
+
if (packet->cp_partial)
pb += packet->rmsg_pgcnt;

@@ -1106,11 +1145,12 @@ static inline int netvsc_send_pkt(
goto exit;
}

- ret = vmbus_sendpacket_pagebuffer(out_channel,
- pb, packet->page_buf_cnt,
- &nvmsg, sizeof(nvmsg),
- req_id);
-
+ netvsc_build_mpb_array(pb, packet->page_buf_cnt,
+ (struct vmbus_packet_mpb_array *)&desc,
+ &desc_size);
+ ret = vmbus_sendpacket_mpb_desc(out_channel,
+ (struct vmbus_packet_mpb_array *)&desc,
+ desc_size, &nvmsg, sizeof(nvmsg), req_id);
if (ret)
netvsc_dma_unmap(ndev_ctx->device_ctx, packet);
} else {
--
2.25.1