linux-kernel - [PATCH 5.11 733/775] virtio/s390: implement virtio-ccw revision 2 correctly

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Date:   Mon,  1 Mar 2021 17:15:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: [PATCH 5.11 733/775] virtio/s390: implement virtio-ccw revision 2 correctly

From: Cornelia Huck <cohuck@...hat.com>

commit 182f709c5cff683e6732d04c78e328de0532284f upstream.

CCW_CMD_READ_STATUS was introduced with revision 2 of virtio-ccw,
and drivers should only rely on it being implemented when they
negotiated at least that revision with the device.

However, virtio_ccw_get_status() issued READ_STATUS for any
device operating at least at revision 1. If the device accepts
READ_STATUS regardless of the negotiated revision (which some
implementations like QEMU do, even though the spec currently does
not allow it), everything works as intended. While a device
rejecting the command should also be handled gracefully, we will
not be able to see any changes the device makes to the status,
such as setting NEEDS_RESET or setting the status to zero after
a completed reset.

We negotiated the revision to at most 1, as we never bumped the
maximum revision; let's do that now and properly send READ_STATUS
only if we are operating at least at revision 2.

Cc: stable@...r.kernel.org
Fixes: 7d3ce5ab9430 ("virtio/s390: support READ_STATUS command for virtio-ccw")
Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Link: https://lore.kernel.org/r/20210216110645.1087321-1-cohuck@redhat.com
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/s390/virtio/virtio_ccw.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/s390/virtio/virtio_ccw.c
+++ b/drivers/s390/virtio/virtio_ccw.c
@@ -117,7 +117,7 @@ struct virtio_rev_info {
 };

 /* the highest virtio-ccw revision we support */
-#define VIRTIO_CCW_REV_MAX 1
+#define VIRTIO_CCW_REV_MAX 2

 struct virtio_ccw_vq_info {
 	struct virtqueue *vq;
@@ -952,7 +952,7 @@ static u8 virtio_ccw_get_status(struct v
 	u8 old_status = vcdev->dma_area->status;
 	struct ccw1 *ccw;

-	if (vcdev->revision < 1)
+	if (vcdev->revision < 2)
 		return vcdev->dma_area->status;

 	ccw = ccw_device_dma_zalloc(vcdev->cdev, sizeof(*ccw));