Patch "scsi: virtio_scsi: Always try to read VPD pages" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

scsi: virtio_scsi: Always try to read VPD pages

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
scsi-virtio_scsi-always-try-to-read-vpd-pages.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Gibson <[email protected]>
Date: Thu, 13 Apr 2017 12:13:00 +1000
Subject: scsi: virtio_scsi: Always try to read VPD pages

From: David Gibson <[email protected]>

[ Upstream commit 25d1d50e23275e141e3a3fe06c25a99f4c4bf4e0 ]

Passed through SCSI targets may have transfer limits which come from the host SCSI controller or something on the host side other than the target itself.

To make this work properly, the hypervisor can adjust the target's VPD information to advertise these limits. But for that to work, the guest has to look at the VPD pages, which we won't do by default if it is an SPC-2 device, even if it does actually support it.

This adds a workaround to address this, forcing devices attached to a virtio-scsi controller to always check the VPD pages. This is modelled on a similar workaround for the storvsc (Hyper-V) SCSI controller, although that exists for slightly different reasons.

A specific case which causes this is a volume from IBM's IPR RAID controller (which presents as an SPC-2 device, although it does support VPD) passed through with qemu's 'scsi-block' device.

[mkp: fixed typo]

---
 drivers/scsi/virtio_scsi.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

@@ -28,6 +28,7 @@
 #include <scsi/scsi_device.h>
 #include <scsi/scsi_cmnd.h>
 #include <scsi/scsi_tcq.h>
+#include <scsi/scsi_devinfo.h>
 #include <linux/seqlock.h>
 
 #define VIRTIO_SCSI_MEMPOOL_SZ 64

@@ -705,6 +706,28 @@ static int virtscsi_device_reset(struct
 	return virtscsi_tmf(vscsi, cmd);
 }
 
+static int virtscsi_device_alloc(struct scsi_device *sdevice)
+{
+	/*
+	 * Passed through SCSI targets (e.g. with qemu's 'scsi-block')
+	 * may have transfer limits which come from the host SCSI
+	 * controller or something on the host side other than the
+	 * target itself.
+	 *
+	 * To make this work properly, the hypervisor can adjust the
+	 * target's VPD information to advertise these limits.  But
+	 * for that to work, the guest has to look at the VPD pages,
+	 * which we won't do by default if it is an SPC-2 device, even
+	 * if it does actually support it.
+	 *
+	 * So, set the blist to always try to read the VPD pages.
+	 */
+	sdevice->sdev_bflags = BLIST_TRY_VPD_PAGES;
+
+	return 0;
+}
+
+
 /**
  * virtscsi_change_queue_depth() - Change a virtscsi target's queue depth
  * @sdev:	Virtscsi target whose queue depth to change

@@ -776,6 +799,7 @@ static struct scsi_host_template virtscs
 	.change_queue_depth = virtscsi_change_queue_depth,
 	.eh_abort_handler = virtscsi_abort,
 	.eh_device_reset_handler = virtscsi_device_reset,
+	.slave_alloc = virtscsi_device_alloc,
 
 	.can_queue = 1024,
 	.dma_boundary = UINT_MAX,

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-ppc-book3s-pr-exit-kvm-on-failed-mapping.patch queue-4.9/scsi-virtio_scsi-always-try-to-read-vpd-pages.patch