From: Simon Horman <ho...@kernel.org> Sent: Wednesday, May 14, 2025 2:38 AM > > On Mon, May 12, 2025 at 05:06:01PM -0700, mhkelle...@gmail.com wrote: > > From: Michael Kelley <mhkli...@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: <sta...@vger.kernel.org> # 6.1.x > > Signed-off-by: Michael Kelley <mhkli...@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
