[PATCH v3 0/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff

[PATCH v3 0/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff

[Radim Krčmář]

v3:
  * fixes off-by-one error in [2/4]
  * moves phys_map changes from [2/4] to [4/4]; [2/4] doesn't carry
    David's r-b to [v2 2/4] because of this change
  * expands a comment in [4/4]

v2: http://www.spinics.net/lists/kvm/msg142414.html
> Removes the capability that let userspace know of changes.

v1: http://www.spinics.net/lists/kvm/msg141944.html
> The problem is described in [4/4].
> 
> [1/4] is a prerequisite to allow a cleanup in [2/4].
> [2/4] hopefully makes [4/4] easier to understand.
> [3/4] fixes mistakes from dealing with the mixed mode.
> [4/4] allows the hotplug and and add a capability for it.


Radim Krčmář (4):
  KVM: x86: use delivery to self in hyperv synic
  KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic_id
  KVM: x86: make interrupt delivery fast and slow path behave the same
  KVM: x86: allow hotplug of VCPU with APIC ID over 0xff

 arch/x86/kvm/hyperv.c |  4 +--
 arch/x86/kvm/lapic.c  | 67 +++++++++++++++++++++++++++++++++++++--------------
 arch/x86/kvm/lapic.h  | 11 ---------
 3 files changed, 51 insertions(+), 31 deletions(-)

-- 
2.11.0

[PATCH v3 1/4] KVM: x86: use delivery to self in hyperv synic

[Radim Krčmář]

Interrupt to self can be sent without knowing the APIC ID.

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2: r-b David
---
 arch/x86/kvm/hyperv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 99cde5220e07..313957ec9a9d 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -305,13 +305,13 @@ static int synic_set_irq(struct kvm_vcpu_hv_synic *synic, u32 sint)
 		return -ENOENT;
 
 	memset(&irq, 0, sizeof(irq));
-	irq.dest_id = kvm_apic_id(vcpu->arch.apic);
+	irq.shorthand = APIC_DEST_SELF;
 	irq.dest_mode = APIC_DEST_PHYSICAL;
 	irq.delivery_mode = APIC_DM_FIXED;
 	irq.vector = vector;
 	irq.level = 1;
 
-	ret = kvm_irq_delivery_to_apic(vcpu->kvm, NULL, &irq, NULL);
+	ret = kvm_irq_delivery_to_apic(vcpu->kvm, vcpu->arch.apic, &irq, NULL);
 	trace_kvm_hv_synic_set_irq(vcpu->vcpu_id, sint, irq.vector, ret);
 	return ret;
 }
-- 
2.11.0

[PATCH v3 2/4] KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic_id

[Radim Krčmář]

There were three calls sites:
 - recalculate_apic_map and kvm_apic_match_physical_addr, where it would
   only complicate implementation of x2APIC hotplug;
 - in apic_debug, where it was still somewhat preserved, but keeping the
   old function just for apic_debug was not worth it

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v3:
 * keep correct max_id = 255 [David]
 * postpone phys_map changes to patch 4 [David]
---
 arch/x86/kvm/lapic.c | 31 ++++++++++++++++++++++---------
 arch/x86/kvm/lapic.h | 11 -----------
 2 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 09edd32b8e42..81cc93580c40 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -115,6 +115,16 @@ static inline int apic_enabled(struct kvm_lapic *apic)
 	(LVT_MASK | APIC_MODE_MASK | APIC_INPUT_POLARITY | \
 	 APIC_LVT_REMOTE_IRR | APIC_LVT_LEVEL_TRIGGER)
 
+static inline u8 kvm_xapic_id(struct kvm_lapic *apic)
+{
+	return kvm_lapic_get_reg(apic, APIC_ID) >> 24;
+}
+
+static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
+{
+	return apic->vcpu->vcpu_id;
+}
+
 static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
 		u32 dest_id, struct kvm_lapic ***cluster, u16 *mask) {
 	switch (map->mode) {
@@ -159,13 +169,13 @@ static void recalculate_apic_map(struct kvm *kvm)
 	struct kvm_apic_map *new, *old = NULL;
 	struct kvm_vcpu *vcpu;
 	int i;
-	u32 max_id = 255;
+	u32 max_id = 255; /* enough space for any xAPIC ID */
 
 	mutex_lock(&kvm->arch.apic_map_lock);
 
 	kvm_for_each_vcpu(i, vcpu, kvm)
 		if (kvm_apic_present(vcpu))
-			max_id = max(max_id, kvm_apic_id(vcpu->arch.apic));
+			max_id = max(max_id, kvm_x2apic_id(vcpu->arch.apic));
 
 	new = kvm_kvzalloc(sizeof(struct kvm_apic_map) +
 	                   sizeof(struct kvm_lapic *) * ((u64)max_id + 1));
@@ -184,12 +194,13 @@ static void recalculate_apic_map(struct kvm *kvm)
 		if (!kvm_apic_present(vcpu))
 			continue;
 
-		aid = kvm_apic_id(apic);
-		ldr = kvm_lapic_get_reg(apic, APIC_LDR);
-
+		aid = apic_x2apic_mode(apic) ? kvm_x2apic_id(apic)
+		                             : kvm_xapic_id(apic);
 		if (aid <= new->max_apic_id)
 			new->phys_map[aid] = apic;
 
+		ldr = kvm_lapic_get_reg(apic, APIC_LDR);
+
 		if (apic_x2apic_mode(apic)) {
 			new->mode |= KVM_APIC_MODE_X2APIC;
 		} else if (ldr) {
@@ -250,6 +261,8 @@ static inline void kvm_apic_set_x2apic_id(struct kvm_lapic *apic, u32 id)
 {
 	u32 ldr = ((id >> 4) << 16) | (1 << (id & 0xf));
 
+	WARN_ON_ONCE(id != apic->vcpu->vcpu_id);
+
 	kvm_lapic_set_reg(apic, APIC_ID, id);
 	kvm_lapic_set_reg(apic, APIC_LDR, ldr);
 	recalculate_apic_map(apic->vcpu->kvm);
@@ -591,9 +604,9 @@ static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda)
 		return true;
 
 	if (apic_x2apic_mode(apic))
-		return mda == kvm_apic_id(apic);
+		return mda == kvm_x2apic_id(apic);
 
-	return mda == SET_APIC_DEST_FIELD(kvm_apic_id(apic));
+	return mda == SET_APIC_DEST_FIELD(kvm_xapic_id(apic));
 }
 
 static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
@@ -1907,9 +1920,9 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vcpu->arch.apic_arb_prio = 0;
 	vcpu->arch.apic_attention = 0;
 
-	apic_debug("%s: vcpu=%p, id=%d, base_msr="
+	apic_debug("%s: vcpu=%p, id=0x%x, base_msr="
 		   "0x%016" PRIx64 ", base_address=0x%0lx.\n", __func__,
-		   vcpu, kvm_apic_id(apic),
+		   vcpu, kvm_lapic_get_reg(apic, APIC_ID),
 		   vcpu->arch.apic_base, apic->base_address);
 }
 
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index e0c80233b3e1..cb16e6fd2330 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -202,17 +202,6 @@ static inline int kvm_lapic_latched_init(struct kvm_vcpu *vcpu)
 	return lapic_in_kernel(vcpu) && test_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
 }
 
-static inline u32 kvm_apic_id(struct kvm_lapic *apic)
-{
-	/* To avoid a race between apic_base and following APIC_ID update when
-	 * switching to x2apic_mode, the x2apic mode returns initial x2apic id.
-	 */
-	if (apic_x2apic_mode(apic))
-		return apic->vcpu->vcpu_id;
-
-	return kvm_lapic_get_reg(apic, APIC_ID) >> 24;
-}
-
 bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector);
 
 void wait_lapic_expire(struct kvm_vcpu *vcpu);
-- 
2.11.0

Re: [PATCH v3 2/4] KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic_id

[David Hildenbrand]

Am 15.12.2016 um 18:06 schrieb Radim Krčmář:
> There were three calls sites:
>  - recalculate_apic_map and kvm_apic_match_physical_addr, where it would
>    only complicate implementation of x2APIC hotplug;
>  - in apic_debug, where it was still somewhat preserved, but keeping the
>    old function just for apic_debug was not worth it
>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

Reviewed-by: David Hildenbrand <david@redhat.com>


-- 

David

[PATCH v3 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same

[Radim Krčmář]

Slow path tried to prevent IPIs from x2APIC VCPUs from being delivered
to xAPIC VCPUs and vice-versa.  Make slow path behave like fast path,
which never distinguished that.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 arch/x86/kvm/lapic.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 81cc93580c40..519b72bbf947 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -606,7 +606,7 @@ static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda)
 	if (apic_x2apic_mode(apic))
 		return mda == kvm_x2apic_id(apic);
 
-	return mda == SET_APIC_DEST_FIELD(kvm_xapic_id(apic));
+	return mda == kvm_xapic_id(apic);
 }
 
 static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
@@ -623,7 +623,6 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
 		       && (logical_id & mda & 0xffff) != 0;
 
 	logical_id = GET_APIC_LOGICAL_ID(logical_id);
-	mda = GET_APIC_DEST_FIELD(mda);
 
 	switch (kvm_lapic_get_reg(apic, APIC_DFR)) {
 	case APIC_DFR_FLAT:
@@ -640,9 +639,9 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
 
 /* 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.
+ *  - Real hardware delivers interrupts destined to x2APIC ID > 0xff to LAPICs
+ *    in xAPIC mode if the "destination & 0xff" matches its xAPIC ID.
+ *    KVM doesn't do that aliasing.
  *
  *  - in-kernel IOAPIC messages have to be delivered directly to
  *    x2APIC, because the kernel does not support interrupt remapping.
@@ -658,13 +657,12 @@ 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 (!vcpu->kvm->arch.x2apic_broadcast_quirk_disabled &&
-	    !ipi && dest_id == APIC_BROADCAST && x2apic_mda)
+	    !ipi && dest_id == APIC_BROADCAST && apic_x2apic_mode(target))
 		return X2APIC_BROADCAST;
 
-	return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
+	return dest_id;
 }
 
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
-- 
2.11.0

Re: [PATCH v3 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same

[David Hildenbrand]

Am 15.12.2016 um 18:06 schrieb Radim Krčmář:
> Slow path tried to prevent IPIs from x2APIC VCPUs from being delivered
> to xAPIC VCPUs and vice-versa.  Make slow path behave like fast path,
> which never distinguished that.
>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

Just to verify:

The GET_APIC_DEST_FIELD(mda) == APIC_BROADCAST is still correct in 
kvm_apic_broadcast() ?


Apart from that thing confusing me, this looks good to me :)

-- 

David

Re: [PATCH v3 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same

[Paolo Bonzini]

On 16/12/2016 17:41, David Hildenbrand wrote:
> 
> Just to verify:
> 
> The GET_APIC_DEST_FIELD(mda) == APIC_BROADCAST is still correct in
> kvm_apic_broadcast() ?

No, it seems wrong.

Paolo

[PATCH v4 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same

[Radim Krčmář]

2016-12-16 17:53+0100, Paolo Bonzini:
> On 16/12/2016 17:41, David Hildenbrand wrote:
>> 
>> Just to verify:
>> 
>> The GET_APIC_DEST_FIELD(mda) == APIC_BROADCAST is still correct in
>> kvm_apic_broadcast() ?
> 
> No, it seems wrong.

Definitely, sending v4 of this patch.
I'll also add broadcast address check into kvm-unit-tests ...
---8<---
Slow path tried to prevent IPIs from x2APIC VCPUs from being delivered
to xAPIC VCPUs and vice-versa.  Make slow path behave like fast path,
which never distinguished that.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v4: fix xAPIC broadcast address detection [David]
---
 arch/x86/kvm/lapic.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 81cc93580c40..dba19cb82c3e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -592,10 +592,8 @@ static void apic_set_tpr(struct kvm_lapic *apic, u32 tpr)
 
 static bool kvm_apic_broadcast(struct kvm_lapic *apic, u32 mda)
 {
-	if (apic_x2apic_mode(apic))
-		return mda == X2APIC_BROADCAST;
-
-	return GET_APIC_DEST_FIELD(mda) == APIC_BROADCAST;
+	return mda == (apic_x2apic_mode(apic) ?
+			X2APIC_BROADCAST : APIC_BROADCAST);
 }
 
 static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda)
@@ -606,7 +604,7 @@ static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda)
 	if (apic_x2apic_mode(apic))
 		return mda == kvm_x2apic_id(apic);
 
-	return mda == SET_APIC_DEST_FIELD(kvm_xapic_id(apic));
+	return mda == kvm_xapic_id(apic);
 }
 
 static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
@@ -623,7 +621,6 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
 		       && (logical_id & mda & 0xffff) != 0;
 
 	logical_id = GET_APIC_LOGICAL_ID(logical_id);
-	mda = GET_APIC_DEST_FIELD(mda);
 
 	switch (kvm_lapic_get_reg(apic, APIC_DFR)) {
 	case APIC_DFR_FLAT:
@@ -640,9 +637,9 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda)
 
 /* 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.
+ *  - Real hardware delivers interrupts destined to x2APIC ID > 0xff to LAPICs
+ *    in xAPIC mode if the "destination & 0xff" matches its xAPIC ID.
+ *    KVM doesn't do that aliasing.
  *
  *  - in-kernel IOAPIC messages have to be delivered directly to
  *    x2APIC, because the kernel does not support interrupt remapping.
@@ -658,13 +655,12 @@ 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 (!vcpu->kvm->arch.x2apic_broadcast_quirk_disabled &&
-	    !ipi && dest_id == APIC_BROADCAST && x2apic_mda)
+	    !ipi && dest_id == APIC_BROADCAST && apic_x2apic_mode(target))
 		return X2APIC_BROADCAST;
 
-	return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
+	return dest_id;
 }
 
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
-- 
2.11.0

Re: [PATCH v4 3/4] KVM: x86: make interrupt delivery fast and slow path behave the same

[David Hildenbrand]

Am 16.12.2016 um 18:07 schrieb Radim Krčmář:
> 2016-12-16 17:53+0100, Paolo Bonzini:
>> On 16/12/2016 17:41, David Hildenbrand wrote:
>>>
>>> Just to verify:
>>>
>>> The GET_APIC_DEST_FIELD(mda) == APIC_BROADCAST is still correct in
>>> kvm_apic_broadcast() ?
>>
>> No, it seems wrong.
>
> Definitely, sending v4 of this patch.
> I'll also add broadcast address check into kvm-unit-tests ...
> ---8<---
> Slow path tried to prevent IPIs from x2APIC VCPUs from being delivered
> to xAPIC VCPUs and vice-versa.  Make slow path behave like fast path,
> which never distinguished that.
>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  v4: fix xAPIC broadcast address detection [David]
> ---
>  arch/x86/kvm/lapic.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
>

Looks good to me.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

David

[PATCH v3 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff

[Radim Krčmář]

LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of
VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI,
but there is no way to uniquely address it using xAPIC.

>From many possible options, we chose the one that also works on real
hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in
xAPIC mode.

KVM intentionally differs from real hardware, because real hardware
(Knights Landing) does just "x2apic_id & 0xff" to decide whether to
accept the interrupt in xAPIC mode and it can deliver one interrupt to
more than one physical destination, e.g. 0x123 to 0x123 and 0x23.

Fixes: 682f732ecf73 ("KVM: x86: bump MAX_VCPUS to 288")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v3:
 * move code that populated physical_map from patch 2 [David]
 * extend a comment kvm_apic_match_physical_addr()
 v2:
 * Do not add capability [David, Paolo]
 * Tag it as a fix [David]
---
 arch/x86/kvm/lapic.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 519b72bbf947..c6758bdc2c24 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -189,15 +189,26 @@ static void recalculate_apic_map(struct kvm *kvm)
 		struct kvm_lapic *apic = vcpu->arch.apic;
 		struct kvm_lapic **cluster;
 		u16 mask;
-		u32 ldr, aid;
+		u32 ldr;
+		u8 xapic_id;
+		u32 x2apic_id;
 
 		if (!kvm_apic_present(vcpu))
 			continue;
 
-		aid = apic_x2apic_mode(apic) ? kvm_x2apic_id(apic)
-		                             : kvm_xapic_id(apic);
-		if (aid <= new->max_apic_id)
-			new->phys_map[aid] = apic;
+		xapic_id = kvm_xapic_id(apic);
+		x2apic_id = kvm_x2apic_id(apic);
+
+		/* Hotplug hack: see kvm_apic_match_physical_addr(), ... */
+		if ((apic_x2apic_mode(apic) || x2apic_id > 0xff) &&
+				x2apic_id <= new->max_apic_id)
+			new->phys_map[x2apic_id] = apic;
+		/*
+		 * ... xAPIC ID of VCPUs with APIC ID > 0xff will wrap-around,
+		 * prevent them from masking VCPUs with APIC ID <= 0xff.
+		 */
+		if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id])
+			new->phys_map[xapic_id] = apic;
 
 		ldr = kvm_lapic_get_reg(apic, APIC_LDR);
 
@@ -606,6 +617,15 @@ static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda)
 	if (apic_x2apic_mode(apic))
 		return mda == kvm_x2apic_id(apic);
 
+	/*
+	 * Hotplug hack: Make LAPIC in xAPIC mode also accept interrupts as if
+	 * it were in x2APIC mode.  Hotplugged VCPUs start in xAPIC mode and
+	 * this allows unique addressing of VCPUs with APIC ID over 0xff.
+	 * The 0xff condition is needed because writeable xAPIC ID.
+	 */
+	if (kvm_x2apic_id(apic) > 0xff && mda == kvm_x2apic_id(apic))
+		return true;
+
 	return mda == kvm_xapic_id(apic);
 }
 
-- 
2.11.0

Re: [PATCH v3 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff

[David Hildenbrand]

Am 15.12.2016 um 18:06 schrieb Radim Krčmář:
> LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of
> VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI,
> but there is no way to uniquely address it using xAPIC.
>
> From many possible options, we chose the one that also works on real
> hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in
> xAPIC mode.
>
> KVM intentionally differs from real hardware, because real hardware
> (Knights Landing) does just "x2apic_id & 0xff" to decide whether to
> accept the interrupt in xAPIC mode and it can deliver one interrupt to
> more than one physical destination, e.g. 0x123 to 0x123 and 0x23.
>
> Fixes: 682f732ecf73 ("KVM: x86: bump MAX_VCPUS to 288")
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

David