Re: [PATCH v3 4/8] qemu: probe mshv capabilities

[Praveen K Paladugu]

On 10/1/2025 4:37 AM, Daniel P. Berrangé wrote:
On Fri, Aug 29, 2025 at 03:28:34PM -0500, Praveen K Paladugu wrote:
Probe mshv capabilities from qemu with QMP commands. Limit probing only
to x86_64 architecture with newer versions of QEMU.

Signed-off-by: Praveen K Paladugu <pra...@linux.microsoft.com>
---
  src/qemu/qemu_capabilities.c | 21 +++++++++++++++++++++
  src/qemu/qemu_monitor.c      | 12 ++++++++++++
  src/qemu/qemu_monitor.h      | 12 +++++++++---
  src/qemu/qemu_monitor_json.c | 32 ++++++++++++++++++++++++++------
  src/qemu/qemu_monitor_json.h | 13 +++++++++----
  5 files changed, 77 insertions(+), 13 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 1e069eb0e5..cc7774a58a 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -3488,6 +3488,22 @@ virQEMUCapsProbeQMPKVMState(virQEMUCaps *qemuCaps,
      return 0;
  }
  
+static int
+virQEMUCapsProbeQMPMSHVState(virQEMUCaps *qemuCaps,
+                            qemuMonitor *mon)
+{
+    bool enabled = false;
+    bool present = false;
+
+    if (qemuMonitorGetMSHVState(mon, &enabled, &present) < 0)
+        return -1;
+
+    if (present && enabled)
+        virQEMUCapsSet(qemuCaps, QEMU_CAPS_MSHV);
+
+    return 0;
+}
+
  #ifdef __APPLE__
  bool
  virQEMUCapsProbeHVF(virQEMUCaps *qemuCaps)
@@ -5795,6 +5811,11 @@ virQEMUCapsInitQMPMonitor(virQEMUCaps *qemuCaps,
      if (virQEMUCapsProbeQMPKVMState(qemuCaps, mon) < 0)
          return -1;
  
+    if (qemuCaps->arch == VIR_ARCH_X86_64 && qemuCaps->version >= 10000092) {
+        if (virQEMUCapsProbeQMPMSHVState(qemuCaps, mon) < 0)
+            return -1;
+    }

This change causes the test suite to break at this point in the series.

   TEST: qemucapabilitiestest
         ........................................
   wrong expected command in /var/home/berrange/src/virt/libvirt/tests/qemucapabilitiesdata/caps_10.1.0_x86_64.replies:24767: : 
{"execute":"query-mshv","id":"libvirt-6"} expected 
{"execute":"qom-list-types","id":"libvirt-6"}

In order to ensure that it is possible to use 'git bisect' without
spurious failures, we aim to have tests pass at every patch in a
series.

More importantly, we generally aim to avoid having version number
checks and instead rely on detected features.

If you introduce a new QEMU_CAPS_QUERY_MSHV capability flag, you
can update the 'virQEMUCapsCommands' array to match 'query-mshv'.

Then at this point in the code you can drop the arch check and
the version check, and instead check QEMU_CAPS_QUERY_MSHV as
a witness for being able to call virQEMUCapsProbeQMPMSHVState.

Possibly still need some updates to the qemucapabilitiesdata
files after doing that in this commit, but not 100% sure.

With regards,
Daniel

Thanks for the feedback Daniel. I will address this bug and rest of the 
comments in my next update.

--
Regards,
Praveen K Paladugu