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authorRadim Krčmář <rkrcmar@redhat.com>2016-07-12 20:09:28 (GMT)
committerPaolo Bonzini <pbonzini@redhat.com>2016-07-14 07:29:34 (GMT)
commitc519265f2aa348b2f1b9ecf8fbe20bb7c0fb102e (patch)
treed8e9820f18f59eb4b6400e768280a88c7e88f50a
parent3713131345fbea291cbd859d248e06ed77815962 (diff)
downloadlinux-c519265f2aa348b2f1b9ecf8fbe20bb7c0fb102e.tar.xz
KVM: x86: add a flag to disable KVM x2apic broadcast quirk
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> [Expand kvm_apic_mda comment. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--Documentation/virtual/kvm/api.txt6
-rw-r--r--arch/x86/include/asm/kvm_host.h1
-rw-r--r--arch/x86/kvm/lapic.c53
-rw-r--r--arch/x86/kvm/x86.c5
-rw-r--r--include/uapi/linux/kvm.h1
5 files changed, 52 insertions, 14 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index e34e51f..c4d2fb0 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3844,12 +3844,18 @@ Returns: 0 on success, -EINVAL when args[0] contains invalid features
Valid feature flags in args[0] are
#define KVM_X2APIC_API_USE_32BIT_IDS (1ULL << 0)
+#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK (1ULL << 1)
Enabling KVM_X2APIC_API_USE_32BIT_IDS 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. Otherwise, KVM treats 0xff
+as a broadcast even in x2APIC mode in order to support physical x2APIC
+without interrupt remapping. This is undesirable in logical mode,
+where 0xff represents CPUs 0-7 in cluster 0.
8. Other capabilities.
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7c00ba3..074b5c7 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 d27a782..a16e0bb 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -616,17 +616,30 @@ 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 KVM local APIC implementation has two quirks:
+ *
+ * - the xAPIC MDA stores the destination at bits 24-31, while this
+ * is not true of struct kvm_lapic_irq's dest_id field. This is
+ * just a quirk in the API and is not problematic.
+ *
+ * - in-kernel IOAPIC messages have to be delivered directly to
+ * x2APIC, because the kernel does not support interrupt remapping.
+ * In order to support broadcast without interrupt remapping, x2APIC
+ * rewrites the destination of non-IPI messages from APIC_BROADCAST
+ * to X2APIC_BROADCAST.
+ *
+ * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. This is
+ * important when userspace wants to use x2APIC-format MSIs, because
+ * APIC_BROADCAST (0xff) is a legal route for "cluster 0, CPUs 0-7".
*/
-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 +649,7 @@ 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 +701,25 @@ static void kvm_apic_disabled_lapic_found(struct kvm *kvm)
}
}
+static bool kvm_apic_is_broadcast_dest(struct kvm *kvm, struct kvm_lapic **src,
+ struct kvm_lapic_irq *irq, struct kvm_apic_map *map)
+{
+ 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 +733,6 @@ 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 +741,7 @@ 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 (!map || kvm_apic_is_broadcast_dest(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 d86f563..f0d2362 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_IDS)
+#define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_IDS | \
+ 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_IDS)
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 f704403..4f8030e 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_IDS (1ULL << 0)
+#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK (1ULL << 1)
#endif /* __LINUX_KVM_H */