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Re: [PATCH v16 08/11] qapi/s390x/cpu topology: set-cpu-topology monitor

From: Pierre Morel
Subject: Re: [PATCH v16 08/11] qapi/s390x/cpu topology: set-cpu-topology monitor command
Date: Mon, 27 Feb 2023 15:11:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0

On 2/27/23 13:15, Nina Schoetterl-Glausch wrote:
On Mon, 2023-02-27 at 11:57 +0100, Pierre Morel wrote:
On 2/24/23 18:15, Nina Schoetterl-Glausch wrote:
On Wed, 2023-02-22 at 15:21 +0100, Pierre Morel wrote:
The modification of the CPU attributes are done through a monitor

It allows to move the core inside the topology tree to optimize
the cache usage in the case the host's hypervisor previously
moved the CPU.

The same command allows to modify the CPU attributes modifiers
like polarization entitlement and the dedicated attribute to notify
the guest if the host admin modified scheduling or dedication of a vCPU.

With this knowledge the guest has the possibility to optimize the
usage of the vCPUs.

The command has a feature unstable for the moment.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
   qapi/machine-target.json |  35 +++++++++
   include/monitor/hmp.h    |   1 +
   hw/s390x/cpu-topology.c  | 154 +++++++++++++++++++++++++++++++++++++++
   hmp-commands.hx          |  17 +++++
   4 files changed, 207 insertions(+)

diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
index ed5fc75381..3a7eb441a3 100644
--- a/hw/s390x/cpu-topology.c
+++ b/hw/s390x/cpu-topology.c
@@ -19,6 +19,12 @@

+void qmp_set_cpu_topology(uint16_t core,
+                         bool has_socket, uint16_t socket,
+                         bool has_book, uint16_t book,
+                         bool has_drawer, uint16_t drawer,
+                         const char *entitlement_str,
+                         bool has_dedicated, bool dedicated,
+                         Error **errp)
+    bool has_entitlement = false;
+    int entitlement;
+    ERRP_GUARD();
+    if (!s390_has_topology()) {
+        error_setg(errp, "This machine doesn't support topology");
+        return;
+    }
+    entitlement = qapi_enum_parse(&CpuS390Entitlement_lookup, entitlement_str,
+                                  -1, errp);
+    if (*errp) {
+        return;
+    }
+    has_entitlement = entitlement >= 0;
Doesn't this allow setting horizontal entitlement? Which shouldn't be possible,
only the guest can do it.

IMHO it does not, the polarization is set by the guest through the PTF
instruction, but entitlement is set by the host.
Yes, so when the guests requests vertical polarization, all cpus have a
(vertical) entitlement assigned and will show up as vertical in STSI.
But now, by using the qmp command, the polarization can be reset to horizontal,
even though the guest didn't ask for it.

Right, I will change this



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