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[Qemu-devel] [PATCH] s390/ipl: Fix spurious errors in virtio

From: Christian Borntraeger
Subject: [Qemu-devel] [PATCH] s390/ipl: Fix spurious errors in virtio
Date: Thu, 23 May 2013 13:51:41 +0200

With the ccw ipl code sometimes an error message like
"virtio: trying to map MMIO memory" or
"Guest moved used index from %u to %u" appeared. Turns out
that the ccw bios did not zero out the vring, which might
cause stale values in avail->idx and friends, especially
on reboot.

Lets zero out the relevant fields. To activate the patch we
need to rebuild s390-ccw.img as well.

Signed-off-by: Christian Borntraeger <address@hidden>
 pc-bios/s390-ccw/virtio.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c
index 5b9e1dc..f438af1 100644
--- a/pc-bios/s390-ccw/virtio.c
+++ b/pc-bios/s390-ccw/virtio.c
@@ -114,8 +114,13 @@ static void vring_init(struct vring *vr, unsigned int num, 
void *p,
     vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + align-1)
                 & ~(align - 1));
+    /* Zero out all relevant field */
+    vr->avail->flags = 0;
+    vr->avail->idx = 0;
     /* We're running with interrupts off anyways, so don't bother */
     vr->used->flags = VRING_USED_F_NO_NOTIFY;
+    vr->used->idx = 0;
     debug_print_addr("init vr", vr);

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