[RFC PATCH 6/7] qemu: force special features enabled for TDX guest

[Zhenzhong Duan]

TDX guest requires some special parameters in qemu command line.
They are "pic=no,kernel_irqchip=split" without which guest fails to
bootup.

PMU has a big impact to the performance of TDX guest. So always
disable PMU except it's forcely enabled.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan at intel.com>
---
 src/qemu/qemu_command.c  | 6 +++++-
 src/qemu/qemu_validate.c | 6 ++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 891d795b02..bffa3fdf10 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -6599,6 +6599,10 @@ qemuBuildCpuCommandLine(virCommand *cmd,
         virTristateSwitch pmu = def->features[VIR_DOMAIN_FEATURE_PMU];
         virBufferAsprintf(&buf, ",pmu=%s",
                           virTristateSwitchTypeToString(pmu));
+    } else if (!def->features[VIR_DOMAIN_FEATURE_PMU] && def->tdx) {
+        /* PMU lead to performance drop if TDX enabled, disable PMU by default */
+        virBufferAsprintf(&buf, ",pmu=%s",
+                          virTristateSwitchTypeToString(VIR_TRISTATE_SWITCH_OFF));
     }
 
     if (def->cpu && def->cpu->cache) {
@@ -6975,7 +6979,7 @@ qemuBuildMachineCommandLine(virCommand *cmd,
     }
 
     if (def->tdx)
-        virBufferAddLit(&buf, ",confidential-guest-support=tdx0,kvm-type=tdx");
+        virBufferAddLit(&buf, ",confidential-guest-support=tdx0,kvm-type=tdx,pic=no");
 
     if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_BLOCKDEV)) {
         if (priv->pflash0)
diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
index 2efd011cc0..3c3a00c7e8 100644
--- a/src/qemu/qemu_validate.c
+++ b/src/qemu/qemu_validate.c
@@ -202,6 +202,12 @@ qemuValidateDomainDefFeatures(const virDomainDef *def,
                     return -1;
                 }
             }
+            if (def->tdx && (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_MACHINE_KERNEL_IRQCHIP)
+                             || def->features[i] != VIR_DOMAIN_IOAPIC_QEMU)) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("TDX guest needs split kernel irqchip"));
+                return -1;
+            }
             break;
 
         case VIR_DOMAIN_FEATURE_HPT:
-- 
2.25.1