linux-kernel - Re: [PATCH v6 2/2] kvm: introduce KVM_MAX_VCPU

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Date:	Tue, 10 May 2016 19:17:22 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>,
	Greg Kurz <gkurz@...ux.vnet.ibm.com>
Cc:	james.hogan@...tec.com, mingo@...hat.com,
	linux-mips@...ux-mips.org, kvm@...r.kernel.org, rkrcmar@...hat.com,
	linux-kernel@...r.kernel.org,
	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	qemu-ppc@...gnu.org, Paul Mackerras <paulus@...ba.org>,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH v6 2/2] kvm: introduce KVM_MAX_VCPU_ID



On 09/05/2016 18:23, Cornelia Huck wrote:
> On Mon, 09 May 2016 18:13:37 +0200
> Greg Kurz <gkurz@...ux.vnet.ibm.com> wrote:
> 
>> The KVM_MAX_VCPUS define provides the maximum number of vCPUs per guest, and
>> also the upper limit for vCPU ids. This is okay for all archs except PowerPC
>> which can have higher ids, depending on the cpu/core/thread topology. In the
>> worst case (single threaded guest, host with 8 threads per core), it limits
>> the maximum number of vCPUS to KVM_MAX_VCPUS / 8.
>>
>> This patch separates the vCPU numbering from the total number of vCPUs, with
>> the introduction of KVM_MAX_VCPU_ID, as the maximal valid value for vCPU ids
>> plus one.
>>
>> The corresponding KVM_CAP_MAX_VCPU_ID allows userspace to validate vCPU ids
>> before passing them to KVM_CREATE_VCPU.
>>
>> This patch only implements KVM_MAX_VCPU_ID with a specific value for PowerPC.
>> Other archs continue to return KVM_MAX_VCPUS instead.
>>
>> Suggested-by: Radim Krcmar <rkrcmar@...hat.com>
>> Signed-off-by: Greg Kurz <gkurz@...ux.vnet.ibm.com>
>> ---
>> v6: - provide cap in generic code (Cornelia)
>>     - change PowerPC limit to threads_per_subcore * KVM_MAX_VCORES (Radim)
>> ---
>>  Documentation/virtual/kvm/api.txt   |   10 ++++++++--
>>  arch/powerpc/include/asm/kvm_host.h |    3 +++
>>  include/linux/kvm_host.h            |    4 ++++
>>  include/uapi/linux/kvm.h            |    1 +
>>  virt/kvm/kvm_main.c                 |    4 +++-
>>  5 files changed, 19 insertions(+), 3 deletions(-)
> 
> Reviewed-by: Cornelia Huck <cornelia.huck@...ibm.com>
> 

Series pushed to kvm/queue, thanks.

Paolo