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[4/4] KVM: x86: enable configurable MAX_VCPU

Message ID 20170413201951.11939-5-rkrcmar@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Radim Krčmář April 13, 2017, 8:19 p.m. UTC
The only user of KVM_MAX_VCPU is switched to kvm->max_vcpu.

The limit could have been INT_MAX as it makes no difference, but there
is no point in making it bigger than KVM_MAX_VCPU_ID.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/irq_comm.c         | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

Comments

Christian Borntraeger April 19, 2017, 8:08 a.m. UTC | #1
On 04/13/2017 10:19 PM, Radim Krčmář wrote:
> The only user of KVM_MAX_VCPU is switched to kvm->max_vcpu.
> 
> The limit could have been INT_MAX as it makes no difference, but there
> is no point in making it bigger than KVM_MAX_VCPU_ID.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/irq_comm.c         | 4 ++--
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 2cc5ec7cc6f5..eeeb88eedabf 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -38,6 +38,7 @@
>  #define KVM_MAX_VCPUS 288
>  #define KVM_SOFT_MAX_VCPUS 240
>  #define KVM_MAX_VCPU_ID 1023
> +#define KVM_CONFIGURABLE_MAX_VCPUS KVM_MAX_VCPU_ID
>  #define KVM_USER_MEM_SLOTS 509
>  /* memory slots that are not exposed to userspace */
>  #define KVM_PRIVATE_MEM_SLOTS 3
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index 4517a4c2ac3a..a7baeb44539a 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -60,7 +60,7 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
>  {
>  	int i, r = -1;
>  	struct kvm_vcpu *vcpu, *lowest = NULL;
> -	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
> +	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(kvm->max_vcpus)];

Doesnt that allow unlimited stack usage?
Radim Krčmář April 24, 2017, 5 p.m. UTC | #2
2017-04-19 10:08+0200, Christian Borntraeger:
> On 04/13/2017 10:19 PM, Radim Krčmář wrote:
>> The only user of KVM_MAX_VCPU is switched to kvm->max_vcpu.
>> 
>> The limit could have been INT_MAX as it makes no difference, but there
>> is no point in making it bigger than KVM_MAX_VCPU_ID.
>> 
>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>> ---
>>  arch/x86/include/asm/kvm_host.h | 1 +
>>  arch/x86/kvm/irq_comm.c         | 4 ++--
>>  2 files changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 2cc5ec7cc6f5..eeeb88eedabf 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -38,6 +38,7 @@
>>  #define KVM_MAX_VCPUS 288
>>  #define KVM_SOFT_MAX_VCPUS 240
>>  #define KVM_MAX_VCPU_ID 1023
>> +#define KVM_CONFIGURABLE_MAX_VCPUS KVM_MAX_VCPU_ID
>>  #define KVM_USER_MEM_SLOTS 509
>>  /* memory slots that are not exposed to userspace */
>>  #define KVM_PRIVATE_MEM_SLOTS 3
>> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
>> index 4517a4c2ac3a..a7baeb44539a 100644
>> --- a/arch/x86/kvm/irq_comm.c
>> +++ b/arch/x86/kvm/irq_comm.c
>> @@ -60,7 +60,7 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
>>  {
>>  	int i, r = -1;
>>  	struct kvm_vcpu *vcpu, *lowest = NULL;
>> -	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
>> +	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(kvm->max_vcpus)];
> 
> Doesnt that allow unlimited stack usage?

Right, it doesn't scale.

kvm->max_vcpus is at most KVM_CONFIGURABLE_MAX_VCPUS, but that will be
bigger than the stack.  I'll allocate the bitmap in v2.

Thanks.
diff mbox

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2cc5ec7cc6f5..eeeb88eedabf 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -38,6 +38,7 @@ 
 #define KVM_MAX_VCPUS 288
 #define KVM_SOFT_MAX_VCPUS 240
 #define KVM_MAX_VCPU_ID 1023
+#define KVM_CONFIGURABLE_MAX_VCPUS KVM_MAX_VCPU_ID
 #define KVM_USER_MEM_SLOTS 509
 /* memory slots that are not exposed to userspace */
 #define KVM_PRIVATE_MEM_SLOTS 3
diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 4517a4c2ac3a..a7baeb44539a 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -60,7 +60,7 @@  int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 {
 	int i, r = -1;
 	struct kvm_vcpu *vcpu, *lowest = NULL;
-	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
+	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(kvm->max_vcpus)];
 	unsigned int dest_vcpus = 0;
 
 	if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
@@ -101,7 +101,7 @@  int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 
 	if (dest_vcpus != 0) {
 		int idx = kvm_vector_to_index(irq->vector, dest_vcpus,
-					dest_vcpu_bitmap, KVM_MAX_VCPUS);
+					dest_vcpu_bitmap, kvm->max_vcpus);
 
 		lowest = kvm_get_vcpu(kvm, idx);
 	}