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Re: [Qemu-devel] [PATCH v3 6/7] s390x/kvm: handle AP instruction interce

From: Tony Krowiak
Subject: Re: [Qemu-devel] [PATCH v3 6/7] s390x/kvm: handle AP instruction interception
Date: Mon, 2 Apr 2018 11:59:10 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0

On 03/26/2018 04:32 AM, David Hildenbrand wrote:
On 16.03.2018 00:24, Tony Krowiak wrote:
If the CPU model indicates that AP facility is installed on
the guest (i.e., -cpu xxxx,ap=on), then the expectation is that
the AP bus running in the guest will initialize; however, if the
AP instructions are not being interpreted by the firmware, then
they will be intercepted and routed back to QEMU for handling.
If a handler is not defined to process the intercepted instruciton,
then an operation exception will be injected into the
guest, in which case the AP bus will not initialize.

There are two situations where AP instructions will not be

1. The guest is not configured with a vfio-ap device (i.e.,
    -device vfio-ap,sysfsdev=$path-to-mdev). The realize function for
    the vfio-ap device enables interpretive execution of AP

2. The guest is a second level guest but the first level guest has
    not enabled interpretive execution.

This patch introduces AP instruction handlers to ensure the AP bus
module initializes on the guest when the AP facility is installed
on the guest but AP instructions are not being interpreted. The logic
incorporated is:

* If the CPU model indicates AP instructions are

   * Set the status response code for the instruction to indicate that
     the APQN contained in the instruction is not valid. This is
     a valid response because there will be no devices configured for
     the guest in any of the above scenarios.

* Else return an error from the handler. This will result in an
   operation being injected into the guest and the AP bus will not
s/operation/operation exception/

   initialize on the guest. That is commensurate with how things work

Signed-off-by: Tony Krowiak <address@hidden>
  hw/vfio/ap.c                 |   45 ++++++++++++++++++++++++++++++++++++++++++
  include/hw/s390x/ap-device.h |    6 +++++
  target/s390x/kvm.c           |   14 +++++++++++++
  3 files changed, 65 insertions(+), 0 deletions(-)

diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
index b397bb1..88e744d 100644
--- a/hw/vfio/ap.c
+++ b/hw/vfio/ap.c
@@ -148,6 +148,51 @@ static void vfio_ap_unrealize(DeviceState *dev, Error 
I think you are missing cpu_synchronize_state(CPU(cpu)) in all of these
I see you negated this in your next response.

+int ap_device_handle_nqap(S390CPU *cpu)
+    CPUS390XState *env = &cpu->env;
+    if (s390_has_feat(S390_FEAT_AP)) {
+        env->regs[1] = 0x10000;
+        return 0;
+    }
+    return -EOPNOTSUPP;
+int ap_device_handle_dqap(S390CPU *cpu)
+    CPUS390XState *env = &cpu->env;
+    if (s390_has_feat(S390_FEAT_AP)) {
+        env->regs[1] = 0x10000;
+        return 0;
+    }
+    return -EOPNOTSUPP;
+int ap_device_handle_pqap(S390CPU *cpu)
+    CPUS390XState *env = &cpu->env;
+    int fc = 4 & (env->regs[0] >> 24);
+    /*
+     * The Query Configuration Information (QCI) function (fc == 4) does not
+     * set a response code in reg 1, so check for that along with the
+     * AP feature.
+     */
+    if ((fc != 4) && s390_has_feat(S390_FEAT_AP)) {
+        env->regs[1] = 0x10000;
+        return 0;
+    }
This would imply an operation exception in case fc==4, which sounds very
Take a look at my response to Pierre for an answer to this one.

Hard to review without access to documentation. (hard to understand why
such stuff is to be kept confidential for decades)
You'll have to talk to the powers that be at IBM about that one :)

+    return -EOPNOTSUPP;
  static Property vfio_ap_properties[] = {
      DEFINE_PROP_STRING("sysfsdev", VFIOAPDevice, vdev.sysfsdev),
diff --git a/include/hw/s390x/ap-device.h b/include/hw/s390x/ap-device.h
index 693df90..d45ae38 100644
--- a/include/hw/s390x/ap-device.h
+++ b/include/hw/s390x/ap-device.h
@@ -11,6 +11,8 @@
  #ifndef HW_S390X_AP_DEVICE_H
  #define HW_S390X_AP_DEVICE_H

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