[PATCH v3 12/14] KVM: x86: add a flag to disable KVM x2apic broadcast quirk

Radim Krčmář
2016-07-12T20:11:30Z

Add KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK as a feature flag to
KVM_CAP_X2APIC_API.

The quirk made KVM interpret 0xff as a broadcast even in x2APIC mode.
The enableable capability is needed in order to support standard x2APIC and
remain backward compatible.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
v3: new

Documentation/virtual/kvm/api.txt | 5 +++++
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/lapic.c | 40 +++++++++++++++++++++++++++++----------
arch/x86/kvm/x86.c | 5 ++++-
include/uapi/linux/kvm.h | 1 +
5 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 10e2bf903e57..c2753ff4a499 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3843,12 +3843,17 @@ Returns: 0 on success, -EINVAL when args[0] contains invalid features
Valid feature flags in args[0] are

#define KVM_X2APIC_API_USE_32BIT_FORMAT (1ULL << 0)
+#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK (1ULL << 1)

Enabling KVM_X2APIC_API_USE_32BIT_FORMAT changes the behavior of
KVM_SET_GSI_ROUTING, KVM_SIGNAL_MSI, KVM_SET_LAPIC, and KVM_GET_LAPIC, allowing
the use of 32-bit APIC IDs. See KVM_CAP_X2APIC_API in their respective
sections.

+KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK must be enabled for x2APIC to work in
+logical mode or with more than 255 VCPUs. A KVM quirk treats 0xff as a
+broadcast even in x2APIC mode (a consequence of allowing physical x2APIC
+without interrupt remapping).

8. Other capabilities.
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f13522f85a1d..25bf9d627c15 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -784,6 +784,7 @@ struct kvm_arch {
struct page *avic_physical_id_table_page;

bool x2apic_format;
+ bool x2apic_broadcast_quirk_disabled;
};

struct kvm_vm_stat {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index d27a7829a4ce..46f1d1c93420 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -619,14 +619,17 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
/* KVM APIC implementation has two quirks
* - dest always begins at 0 while xAPIC MDA has offset 24,
* - IOxAPIC messages have to be delivered (directly) to x2APIC.
+ *
+ * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API.
*/
-static u32 kvm_apic_mda(unsigned int dest_id, struct kvm_lapic *source,
- struct kvm_lapic *target)
+static u32 kvm_apic_mda(struct kvm_vcpu *vcpu, unsigned int dest_id,
+ struct kvm_lapic *source, struct kvm_lapic *target)
{
bool ipi = source != NULL;
bool x2apic_mda = apic_x2apic_mode(ipi ? source : target);

- if (!ipi && dest_id == APIC_BROADCAST && x2apic_mda)
+ if (!vcpu->kvm->arch.x2apic_broadcast_quirk_disabled &&
+ !ipi && dest_id == APIC_BROADCAST && x2apic_mda)
return X2APIC_BROADCAST;

return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
@@ -636,7 +639,7 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
int short_hand, unsigned int dest, int dest_mode)
{
struct kvm_lapic *target = vcpu->arch.apic;
- u32 mda = kvm_apic_mda(dest, source, target);
+ u32 mda = kvm_apic_mda(vcpu, dest, source, target);

apic_debug("target %p, source %p, dest 0x%x, "
"dest_mode 0x%x, short_hand 0x%x\n",
@@ -688,6 +691,28 @@ static void kvm_apic_disabled_lapic_found(struct kvm *kvm)
}
}

+static bool kvm_apic_map_need_slowpath(struct kvm *kvm, struct kvm_lapic **src,
+ struct kvm_lapic_irq *irq, struct kvm_apic_map *map)
+{
+ if (!map)
+ return true;
+
+ if (kvm->arch.x2apic_broadcast_quirk_disabled) {
+ if ((irq->dest_id == APIC_BROADCAST &&
+ map->mode != KVM_APIC_MODE_X2APIC))
+ return true;
+ if (irq->dest_id == X2APIC_BROADCAST)
+ return true;
+ } else {
+ bool x2apic_ipi = src && *src && apic_x2apic_mode(*src);
+ if (irq->dest_id == (x2apic_ipi ?
+ X2APIC_BROADCAST : APIC_BROADCAST))
+ return true;
+ }
+
+ return false;
+}
+
/* Return true if the interrupt can be handled by using *bitmap as index mask
* for valid destinations in *dst array.
* Return false if kvm_apic_map_get_dest_lapic did nothing useful.
@@ -701,7 +726,6 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm,
unsigned long *bitmap)
{
int i, lowest;
- bool x2apic_ipi;

if (irq->shorthand == APIC_DEST_SELF && src) {
*dst = src;
@@ -710,11 +734,7 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm,
} else if (irq->shorthand)
return false;

- x2apic_ipi = src && *src && apic_x2apic_mode(*src);
- if (irq->dest_id == (x2apic_ipi ? X2APIC_BROADCAST : APIC_BROADCAST))
- return false;
-
- if (!map)
+ if (kvm_apic_map_need_slowpath(kvm, src, irq, map))
return false;

if (irq->dest_mode == APIC_DEST_PHYSICAL) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 330276315daa..4bab85f82a96 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -90,7 +90,8 @@ static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
#define VM_STAT(x) offsetof(struct kvm, stat.x), KVM_STAT_VM
#define VCPU_STAT(x) offsetof(struct kvm_vcpu, stat.x), KVM_STAT_VCPU

-#define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_FORMAT)
+#define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_FORMAT | \
+ KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)

static void update_cr8_intercept(struct kvm_vcpu *vcpu);
static void process_nmi(struct kvm_vcpu *vcpu);
@@ -3811,6 +3812,8 @@ split_irqchip_unlock:

if (cap->args[0] & KVM_X2APIC_API_USE_32BIT_FORMAT)
kvm->arch.x2apic_format = true;
+ if (cap->args[0] & KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)
+ kvm->arch.x2apic_broadcast_quirk_disabled = true;

r = 0;
break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index b6de3febabaa..13b30dfd93b2 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1315,5 +1315,6 @@ struct kvm_assigned_msix_entry {
};

#define KVM_X2APIC_API_USE_32BIT_FORMAT (1ULL << 0)
+#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK (1ULL << 1)

#endif /* __LINUX_KVM_H */
--
2.9.0