From: Simon Horman horms@kernel.org Sent: Wednesday, May 14, 2025 2:38 AM
On Mon, May 12, 2025 at 05:06:01PM -0700, mhkelley58@gmail.com wrote:
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.
Hi Michael,
Is there a guarantee that this constraint is met. And moreover, is there a guarantee that all of the entries will fit in desc? I am slightly concerned that there may be an overrun lurking here.
It is indeed up to the caller to ensure that the pb array is properly constructed. netvsc_build_mpb_array() doesn't do additional validation. There are only two sources of the pb array, both of which do the right thing, so additional validation seemed redundant.
An overrun is a concern, but again the callers do the right thing. As described in my response to Patch 3 of the series, netvsc_xmit() counts the number of pages ahead of time, and makes sure the count is within the limit of the amount space allocated in the "desc" argument to netvsc_build_mpb_array().
Michael