From 6b19062226ecebf63d2d0b0ff05b5bcfa7a05818 Mon Sep 17 00:00:00 2001
From: Thomas Huth <thuth@redhat.com>
Date: Thu, 10 Dec 2020 08:32:40 -0500
Subject: [PATCH 4/5] pc-bios: s390x: Ensure Read IPL memory is clean

RH-Author: Thomas Huth <thuth@redhat.com>
Message-id: <20201210083241.173509-4-thuth@redhat.com>
Patchwork-id: 100372
O-Subject: [RHEL-8.4.0 qemu-kvm PATCH 3/4] pc-bios: s390x: Ensure Read IPL memory is clean
Bugzilla: 1903135
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: Jens Freimann <jfreimann@redhat.com>
RH-Acked-by: David Hildenbrand <david@redhat.com>

From: Eric Farman <farman@linux.ibm.com>

If, for example, we boot off a virtio device and chreipl to a vfio-ccw
device, the space at lowcore will be non-zero. We build a Read IPL CCW
at address zero, but it will have leftover PSW data that will conflict
with the Format-0 CCW being generated:

0x0: 00080000 80010000
       ------ Ccw0.cda
              -- Ccw0.chainData
                -- Reserved bits

The data address will be overwritten with the correct value (0x0), but
the apparent data chain bit will cause subsequent memory to be used as
the target of the data store, which may not be where we expect (0x0).

Clear out this space when we boot from DASD, so that we know it exists
exactly as we expect.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Jason J. Herne <jjherne@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@de.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20201120160117.59366-2-farman@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit d8e5bbdd0d6fa8d9b5ac15de62c87105d92ff558)
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 pc-bios/s390-ccw/dasd-ipl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pc-bios/s390-ccw/dasd-ipl.c b/pc-bios/s390-ccw/dasd-ipl.c
index 0fc879bb8e8..71cbae2f16e 100644
--- a/pc-bios/s390-ccw/dasd-ipl.c
+++ b/pc-bios/s390-ccw/dasd-ipl.c
@@ -100,6 +100,9 @@ static void make_readipl(void)
 {
     Ccw0 *ccwIplRead = (Ccw0 *)0x00;
 
+    /* Clear out any existing data */
+    memset(ccwIplRead, 0, sizeof(Ccw0));
+
     /* Create Read IPL ccw at address 0 */
     ccwIplRead->cmd_code = CCW_CMD_READ_IPL;
     ccwIplRead->cda = 0x00; /* Read into address 0x00 in main memory */
-- 
2.27.0