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[v2,1/2] pc-bios: s390x: Ensure Read IPL memory is clean

Message ID 20201120160117.59366-2-farman@linux.ibm.com
State New
Headers show
Series pc-bios/s390 fixes for reboot-to-vfio-ccw | expand

Commit Message

Eric Farman Nov. 20, 2020, 4:01 p.m. UTC 
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>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Janosch Frank <frankja@de.ibm.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
---
 pc-bios/s390-ccw/dasd-ipl.c | 3 +++
 1 file changed, 3 insertions(+)
diff mbox series

Patch

diff --git a/pc-bios/s390-ccw/dasd-ipl.c b/pc-bios/s390-ccw/dasd-ipl.c
index 0fc879bb8e..71cbae2f16 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 */