[PATCH] KVM: x86: Increase the "hard" max VCPU limit

[PATCH] KVM: x86: Increase the "hard" max VCPU limit

[Chegu Vinod]

KVM guests today use 8bit APIC ids allowing for 256 ID's. Reserving one
ID for Broadcast interrupts should leave 255 ID's. In case of KVM there
is no need for reserving another ID for IO-APIC so the hard max limit for
VCPUS can be increased from 254 to 255. (This was confirmed by Gleb Natapov
http://article.gmane.org/gmane.comp.emulators.kvm.devel/99713  )

Signed-off-by: Chegu Vinod <chegu_vinod@hp.com>
---
 arch/x86/include/asm/kvm_host.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4979778..bc57bfa 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -31,7 +31,7 @@
 #include <asm/msr-index.h>
 #include <asm/asm.h>
 
-#define KVM_MAX_VCPUS 254
+#define KVM_MAX_VCPUS 255
 #define KVM_SOFT_MAX_VCPUS 160
 #define KVM_USER_MEM_SLOTS 125
 /* memory slots that are not exposed to userspace */
-- 
1.7.1

Re: [PATCH] KVM: x86: Increase the "hard" max VCPU limit

[Gleb Natapov]

On Sat, Apr 27, 2013 at 06:31:04PM -0700, Chegu Vinod wrote:
> KVM guests today use 8bit APIC ids allowing for 256 ID's. Reserving one
> ID for Broadcast interrupts should leave 255 ID's. In case of KVM there
> is no need for reserving another ID for IO-APIC so the hard max limit for
> VCPUS can be increased from 254 to 255. (This was confirmed by Gleb Natapov
> http://article.gmane.org/gmane.comp.emulators.kvm.devel/99713  )
> 
> Signed-off-by: Chegu Vinod <chegu_vinod@hp.com>
Applied, thanks.

> ---
>  arch/x86/include/asm/kvm_host.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4979778..bc57bfa 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -31,7 +31,7 @@
>  #include <asm/msr-index.h>
>  #include <asm/asm.h>
>  
> -#define KVM_MAX_VCPUS 254
> +#define KVM_MAX_VCPUS 255
>  #define KVM_SOFT_MAX_VCPUS 160
>  #define KVM_USER_MEM_SLOTS 125
>  /* memory slots that are not exposed to userspace */
> -- 
> 1.7.1

--
			Gleb.