intel_iommu: reject broken EIM

Cluster x2APIC cannot work without KVM's x2apic API when the maximal
APIC ID is greater than 8 and only KVM's LAPIC can support x2APIC, so we
forbid other APICs and also the old KVM case with less than 9, to
simplify the code.

There is no point in enabling EIM in forbidden APICs, so we keep it
enabled only for the KVM APIC;  unconditionally, because making the
option depend on KVM version would be a maintanance burden.

Old QEMUs would enable eim whenever intremap was on, which would trick
guests into thinking that they can enable cluster x2APIC even if any
interrupt destination would get clamped to 8 bits.
Depending on your configuration, QEMU could notice that the destination
LAPIC is not present and report it with a very non-obvious:

  KVM: injection failed, MSI lost (Operation not permitted)

Or the guest could say something about unexpected interrupts, because
clamping leads to aliasing so interrupts were being delivered to
incorrect VCPUs.

KVM_X2APIC_API is the feature that allows us to enable EIM for KVM.

QEMU 2.7 allowed EIM whenever interrupt remapping was enabled.  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 "x-buggy-eim=on".

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index a70aa8494ed1f19d31b6e7512a90511feeae555a..1655a65bced868b0c2f346812eca18ee8ed79681 100644 (file)
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -34,6 +34,7 @@
 #include "hw/pci-host/q35.h"
 #include "sysemu/kvm.h"
 #include "hw/i386/apic_internal.h"
+#include "kvm_i386.h"
 
 /*#define DEBUG_INTEL_IOMMU*/
 #ifdef DEBUG_INTEL_IOMMU
@@ -2015,6 +2016,7 @@ 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("x-buggy-eim", IntelIOMMUState, buggy_eim, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -2484,9 +2486,21 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
     }
 
     if (s->intr_eim == ON_OFF_AUTO_AUTO) {
-        s->intr_eim = x86_iommu->intr_supported ?
+        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 && !s->buggy_eim) {
+        if (!kvm_irqchip_in_kernel()) {
+            error_setg(errp, "eim=on requires accel=kvm,kernel-irqchip=split");
+            return false;
+        }
+        if (!kvm_enable_x2apic()) {
+            error_setg(errp, "eim=on requires support on the KVM side"
+                             "(X2APIC_API, first shipped in v4.7)");
+            return false;
+        }
+    }
 
     return true;
 }

diff --git a/include/hw/compat.h b/include/hw/compat.h
index ef3fae3e1beaccdd89d815497e741dccae7eeb8d..0f06e113bee2cf4e86209063a721623ae644308a 100644 (file)
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -14,6 +14,10 @@
         .driver   = "ioapic",\
         .property = "version",\
         .value    = "0x11",\
+    },{\
+        .driver   = "intel-iommu",\
+        .property = "x-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 b5ac60927b1fe86335e9d74030d59d249b94d8e5..1989c1eec10a65e2d903ea6a24ca86afc6ca70d9 100644 (file)
--- 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,

diff --git a/target-i386/kvm-stub.c b/target-i386/kvm-stub.c
index cdf15061091df6c960bca738ea2f7fc05d597e7c..bda4dc2f0c571a7e8051e166a57fdbeaed191dd2 100644 (file)
--- a/target-i386/kvm-stub.c
+++ b/target-i386/kvm-stub.c
@@ -25,6 +25,11 @@ bool kvm_has_smm(void)
     return 1;
 }
 
+bool kvm_enable_x2apic(void)
+{
+    return false;
+}
+
 /* This function is only called inside conditionals which we
  * rely on the compiler to optimize out when CONFIG_KVM is not
  * defined.

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index ee1f53e5695358b0608e244587476100ac953aa4..0fd664648665f7b9354383cf0ea4289b78c283e7 100644 (file)
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -122,6 +122,19 @@ bool kvm_allows_irq0_override(void)
     return !kvm_irqchip_in_kernel() || kvm_has_gsi_routing();
 }
 
+static bool kvm_x2apic_api_set_flags(uint64_t flags)
+{
+    KVMState *s = KVM_STATE(current_machine->accelerator);
+
+    return !kvm_vm_enable_cap(s, KVM_CAP_X2APIC_API, 0, flags);
+}
+
+bool kvm_enable_x2apic(void)
+{
+    return kvm_x2apic_api_set_flags(KVM_X2APIC_API_USE_32BIT_IDS |
+                                    KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK);
+}
+
 static int kvm_get_tsc(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);

diff --git a/target-i386/kvm_i386.h b/target-i386/kvm_i386.h
index 36407e0a5dc77cd92bc64e0303ebc4a28c770bab..5c369b1c5b402da5d3c5c397fa6cbde242bd9ebd 100644 (file)
--- a/target-i386/kvm_i386.h
+++ b/target-i386/kvm_i386.h
@@ -43,4 +43,5 @@ int kvm_device_msix_deassign(KVMState *s, uint32_t dev_id);
 
 void kvm_put_apicbase(X86CPU *cpu, uint64_t value);
 
+bool kvm_enable_x2apic(void);
 #endif