[PATCH 1/1] scsi: storvsc: Limit max_sectors for virtual Fibre Channel devices

[Michael Kelley]

The Hyper-V host is queried to get the max transfer size that it
supports, and this value is used to set max_sectors for the synthetic
SCSI controller.  However, this max transfer size may be too large
for virtual Fibre Channel devices, which are limited to 512 Kbytes.
If a larger transfer size is used with a vFC device, Hyper-V always
returns an error, and storvsc logs a message like this where the SRB
status and SCSI status are both zero:

hv_storvsc <GUID>: tag#197 cmd 0x8a status: scsi 0x0 srb 0x0 hv 0xc0000001

Add logic to limit the max transfer size to 512 Kbytes for vFC devices.

Fixes: 1d3e0980782f ("scsi: storvsc: Correct reporting of Hyper-V I/O size limits")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
---
 drivers/scsi/storvsc_drv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 7f12d93..f282321 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -366,6 +366,7 @@ enum storvsc_request_type {
 #define STORVSC_FC_MAX_LUNS_PER_TARGET			255
 #define STORVSC_FC_MAX_TARGETS				128
 #define STORVSC_FC_MAX_CHANNELS				8
+#define STORVSC_FC_MAX_XFER_SIZE			((u32)(512 * 1024))
 
 #define STORVSC_IDE_MAX_LUNS_PER_TARGET			64
 #define STORVSC_IDE_MAX_TARGETS				1
@@ -2006,6 +2007,9 @@ static int storvsc_probe(struct hv_device *device,
 	 * protecting it from any weird value.
 	 */
 	max_xfer_bytes = round_down(stor_device->max_transfer_bytes, HV_HYP_PAGE_SIZE);
+	if (is_fc)
+		max_xfer_bytes = min(max_xfer_bytes, STORVSC_FC_MAX_XFER_SIZE);
+
 	/* max_hw_sectors_kb */
 	host->max_sectors = max_xfer_bytes >> 9;
 	/*
-- 
1.8.3.1