[Qemu-devel] [PATCH v2] spapr: check smp_threads <= vsmt

[Laurent Vivier <lvivier@redhat.com>]

We ignore silently the value of smp_threads when we set
the default VSMT value, and if smp_threads is greater than VSMT
kernel is going into trouble later.

Fixes: 8904e5a750
("spapr: Adjust default VSMT value for better migration compatibility")

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---

Notes:
    v2: display a specific error message when the default VSMT is used
        fix subject

 hw/ppc/spapr.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 32a876be56..11de276cd5 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2311,6 +2311,12 @@ static void spapr_set_vsmt_mode(sPAPRMachineState *spapr, Error **errp)
          * overwhelmingly common case in production systems.
          */
         spapr->vsmt = 8;
+        if (spapr->vsmt < smp_threads) {
+            error_setg(&local_err, "Cannot support %d threads/core"
+                         " because it must be <= to default VSMT mode (%d)",
+                         smp_threads, spapr->vsmt);
+            goto out;
+        }
     }
 
     /* KVM: If necessary, set the SMT mode: */
-- 
2.14.3