linux-kernel - [PATCH] hv_utils: Set the maximum packet size for VSS driver to the length of the receive buffer

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Date:   Wed, 25 Aug 2021 15:38:57 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linux-hyperv@...r.kernel.org
Cc:     Andres Beltran <lkmlabelt@...il.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@...il.com>,
        Dexuan Cui <decui@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] hv_utils: Set the maximum packet size for VSS driver to the length of the receive buffer

Commit adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out
of the ring buffer") introduced a notion of maximum packet size and for
KVM and FCOPY drivers set it to the length of the receive buffer. VSS
driver wasn't updated, this means that the maximum packet size is now
VMBUS_DEFAULT_MAX_PKT_SIZE (4k). Apparently, this is not enough. I'm
observing a packet of 6304 bytes which is being truncated to 4096. When
VSS driver tries to read next packet from ring buffer it starts from the
wrong offset and receives garbage.

Set the maximum packet size to 'HV_HYP_PAGE_SIZE * 2' in VSS driver. This
matches the length of the receive buffer and is in line with other utils
drivers.

Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer")
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 drivers/hv/hv_snapshot.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index 2267bd4c3472..6018b9d1b1fb 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -375,6 +375,7 @@ hv_vss_init(struct hv_util_service *srv)
 	}
 	recv_buffer = srv->recv_buffer;
 	vss_transaction.recv_channel = srv->channel;
+	vss_transaction.recv_channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;

 	/*
 	 * When this driver loads, the user level daemon that
-- 
2.31.1