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Re: [PATCH v15 06/11] s390x/cpu topology: interception of PTF instructio

From: Thomas Huth
Subject: Re: [PATCH v15 06/11] s390x/cpu topology: interception of PTF instruction
Date: Mon, 6 Feb 2023 12:38:08 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0

On 01/02/2023 14.20, Pierre Morel wrote:
When the host supports the CPU topology facility, the PTF
instruction with function code 2 is interpreted by the SIE,
provided that the userland hypervizor activates the interpretation


by using the KVM_CAP_S390_CPU_TOPOLOGY KVM extension.

The PTF instructions with function code 0 and 1 are intercepted
and must be emulated by the userland hypervizor.


During RESET all CPU of the configuration are placed in
horizontal polarity.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
   * s390_topology_reset:
   * Generic reset for CPU topology, calls s390_topology_reset()
   * s390_topology_reset() to reset the kernel Modified Topology
   * change record.
+ * Then set global and all CPUs polarity to POLARITY_HORIZONTAL.

You describe here already what's going to happen...

  void s390_topology_reset(void)
+    /* Set global polarity to POLARITY_HORIZONTAL */

... then here again ...

+    s390_topology.polarity = POLARITY_HORIZONTAL;

... and the code is (fortunately) also very self-exaplaining...

+    /* Set all CPU polarity to POLARITY_HORIZONTAL */
+    s390_topology_set_cpus_polarity(POLARITY_HORIZONTAL);

... so I'd rather drop the two comments within the function body.


(rest of the patch looks fine to me)


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