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From db20a3f422ca948784aa74375d1977b7d0a1c7ed Mon Sep 17 00:00:00 2001
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From: Cornelia Huck <cohuck@redhat.com>
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Date: Tue, 15 May 2018 07:33:45 +0000
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Subject: s390x/css: disabled subchannels cannot be status pending
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The 3270 code will try to post an attention interrupt when the
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3270 emulator (e.g. x3270) attaches. If the guest has not yet
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enabled the subchannel for the 3270 device, we will present a spurious
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cc 1 (status pending) when it uses msch on it later on, e.g. when
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trying to enable the subchannel.
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To fix this, just don't do anything in css_conditional_io_interrupt()
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if the subchannel is not enabled. The 3270 code will work fine with
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that, and the other user of this function (virtio-ccw) never
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attempts to post an interrupt for a disabled device to begin with.
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CC: qemu-stable@nongnu.org
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Reported-by: Thomas Huth <thuth@redhat.com>
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Tested-by: Thomas Huth <thuth@redhat.com>
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Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
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Acked-by: Halil Pasic <pasic@linux.ibm.com>
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Reviewed-by: David Hildenbrand <david@redhat.com>
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Signed-off-by: Cornelia Huck <cohuck@redhat.com>
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(cherry picked from commit 6e9c893ecd00afd5344c35d0d0ded50eaa0938f6)
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---
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hw/s390x/css.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/hw/s390x/css.c b/hw/s390x/css.c
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index 301bf17..56c3fa8 100644
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--- a/hw/s390x/css.c
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+++ b/hw/s390x/css.c
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@@ -617,6 +617,14 @@ void css_inject_io_interrupt(SubchDev *sch)
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void css_conditional_io_interrupt(SubchDev *sch)
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{
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/*
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+ * If the subchannel is not enabled, it is not made status pending
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+ * (see PoP p. 16-17, "Status Control").
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+ */
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+ if (!(sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA)) {
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+ return;
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+ }
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+
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+ /*
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* If the subchannel is not currently status pending, make it pending
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* with alert status.
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*/
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--
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1.8.3.1
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