[PATCH 4.15 086/168] uio_hv_generic: check that host supports monitor page

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Hemminger <step...@networkplumber.org>


[ Upstream commit 06028d15177a1b406b7b075ea47c6a352732f23a ]

In order for userspace application to signal host, it needs the
host to support the monitor page property. Check for the flag
and fail if this is not supported.

Signed-off-by: Stephen Hemminger <sthem...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/uio/uio_hv_generic.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/uio/uio_hv_generic.c
+++ b/drivers/uio/uio_hv_generic.c
@@ -124,6 +124,13 @@ hv_uio_probe(struct hv_device *dev,
        if (ret)
                goto fail;
 
+       /* Communicating with host has to be via shared memory not hypercall */
+       if (!dev->channel->offermsg.monitor_allocated) {
+               dev_err(&dev->device, "vmbus channel requires hypercall\n");
+               ret = -ENOTSUPP;
+               goto fail_close;
+       }
+
        dev->channel->inbound.ring_buffer->interrupt_mask = 1;
        set_channel_read_mode(dev->channel, HV_CALL_DIRECT);