[Qemu-devel] [PATCH v4 7/8] intel_iommu: keep buggy EIM enabled in 2.7 machine type

["Radim Krčmář" <rkrcmar@redhat.com>]

QEMU 2.7 allowed EIM even in configurations that were forbidden in the
last patch because they were not working, like old KVM or userspace
APIC.  In order to keep backward compatibility, we again allow guests to
misbehave in non-obvious ways, and make it the default for old machine
types.

A user can enable the buggy mode it with "buggy_eim=on", which is weird,
but I don't know how to add a private property.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
v4:
 * use a device property [Igor]
 * clarify the last sentence of the commit message
v3: shorten the code [Peter]
---
 hw/i386/intel_iommu.c         | 7 ++++---
 include/hw/compat.h           | 4 ++++
 include/hw/i386/intel_iommu.h | 1 +
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index efb018b85544..fe257e8357b4 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -2015,6 +2015,7 @@ static Property vtd_properties[] = {
     DEFINE_PROP_UINT32("version", IntelIOMMUState, version, 0),
     DEFINE_PROP_ON_OFF_AUTO("eim", IntelIOMMUState, intr_eim,
                             ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_BOOL("buggy_eim", IntelIOMMUState, buggy_eim, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -2473,11 +2474,11 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
     }
 
     if (s->intr_eim == ON_OFF_AUTO_AUTO) {
-        s->intr_eim = x86_iommu->intr_supported && kvm_irqchip_in_kernel() ?
+        s->intr_eim = (kvm_irqchip_in_kernel() || s->buggy_eim)
+                      && x86_iommu->intr_supported ?
                                               ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
     }
-
-    if (s->intr_eim == ON_OFF_AUTO_ON) {
+    if (s->intr_eim == ON_OFF_AUTO_ON && !s->buggy_eim) {
         if (kvm_irqchip_in_kernel() && !kvm_enable_x2apic()) {
             error_setg(errp, "eim=on requires support on the KVM side"
                              "(X2APIC_API, first shipped in v4.7)");
diff --git a/include/hw/compat.h b/include/hw/compat.h
index 46412b229a70..43b50065e082 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -10,6 +10,10 @@
         .driver   = "ioapic",\
         .property = "version",\
         .value    = "0x11",\
+    },{\
+        .driver   = "intel-iommu",\
+        .property = "buggy_eim",\
+        .value    = "true",\
     },
 
 #define HW_COMPAT_2_6 \
diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
index b5ac60927b1f..1989c1eec10a 100644
--- a/include/hw/i386/intel_iommu.h
+++ b/include/hw/i386/intel_iommu.h
@@ -290,6 +290,7 @@ struct IntelIOMMUState {
     uint32_t intr_size;             /* Number of IR table entries */
     bool intr_eime;                 /* Extended interrupt mode enabled */
     OnOffAuto intr_eim;             /* Toggle for EIM cabability */
+    bool buggy_eim;                 /* Force buggy EIM unless eim=off */
 };
 
 /* Find the VTD Address space associated with the given bus pointer,
-- 
2.10.0