Commit 6de74d10 authored by Michael Kelley's avatar Michael Kelley Committed by Wei Liu
Browse files

hv_utils: Add comment about max VMbus packet size in VSS driver 



The VSS driver allocates a VMbus receive buffer significantly
larger than sizeof(hv_vss_msg), with no explanation. To help
prevent future mistakes, add a #define and comment about why
this is done.

No functional change.

Signed-off-by: default avatarMichael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1644423070-75125-1-git-send-email-mikelley@microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
parent 4ee52458

drivers/hv/hv_snapshot.c

+5 −2
Original line number Diff line number Diff line
@@ -31,6 +31,9 @@ static const int fw_versions[] = { 
	UTIL_FW_VERSION

};



/* See comment with struct hv_vss_msg regarding the max VMbus packet size */

#define VSS_MAX_PKT_SIZE (HV_HYP_PAGE_SIZE * 2)



/*

 * Timeout values are based on expecations from host

 */
@@ -298,7 +301,7 @@ void hv_vss_onchannelcallback(void *context) 
	if (vss_transaction.state > HVUTIL_READY)

		return;



	if (vmbus_recvpacket(channel, recv_buffer, HV_HYP_PAGE_SIZE * 2, &recvlen, &requestid)) {

	if (vmbus_recvpacket(channel, recv_buffer, VSS_MAX_PKT_SIZE, &recvlen, &requestid)) {

		pr_err_ratelimited("VSS request received. Could not read into recv buf\n");

		return;

	}
@@ -375,7 +378,7 @@ 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;

	vss_transaction.recv_channel->max_pkt_size = VSS_MAX_PKT_SIZE;



	/*

	 * When this driver loads, the user level daemon that

include/uapi/linux/hyperv.h

+11 −0
Original line number Diff line number Diff line
@@ -90,6 +90,17 @@ struct hv_vss_check_dm_info { 
	__u32 flags;

} __attribute__((packed));



/*

 * struct hv_vss_msg encodes the fields that the Linux VSS

 * driver accesses. However, FREEZE messages from Hyper-V contain

 * additional LUN information that Linux doesn't use and are not

 * represented in struct hv_vss_msg. A received FREEZE message may

 * be as large as 6,260 bytes, so the driver must allocate at least

 * that much space, not sizeof(struct hv_vss_msg). Other messages

 * such as AUTO_RECOVER may be as large as 12,500 bytes. However,

 * because the Linux VSS driver responds that it doesn't support

 * auto-recovery, it should not receive such messages.

 */

struct hv_vss_msg {

	union {

		struct hv_vss_hdr vss_hdr;