linux-kernel - Re: [PATCH v11 017/113] KVM: Support KVM_CAP_MAX_VCPUS for KVM_ENABLE

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Message-ID: <20230227212835.GG4175971@ls.amr.corp.intel.com>
Date:   Mon, 27 Feb 2023 13:28:35 -0800
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Zhi Wang <zhi.wang.linux@...il.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v11 017/113] KVM: Support KVM_CAP_MAX_VCPUS for
 KVM_ENABLE_CAP

On Fri, Jan 13, 2023 at 02:55:07PM +0200,
Zhi Wang <zhi.wang.linux@...il.com> wrote:

> On Thu, 12 Jan 2023 08:31:25 -0800
> isaku.yamahata@...el.com wrote:
> 
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > TDX attestation includes the maximum number of vcpu that the guest can
> > accommodate.  For that, the maximum number of vcpu needs to be specified
> > instead of constant, KVM_MAX_VCPUS.  Make KVM_ENABLE_CAP support
> > KVM_CAP_MAX_VCPUS.
> > 
> > Suggested-by: Sagi Shahar <sagis@...gle.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >  virt/kvm/kvm_main.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index a235b628b32f..1cfa7da92ad0 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -4945,7 +4945,27 @@ static int kvm_vm_ioctl_enable_cap_generic(struct
> > kvm *kvm, }
> >  
> >  		mutex_unlock(&kvm->slots_lock);
> > +		return r;
> > +	}
> > +	case KVM_CAP_MAX_VCPUS: {
> 
> Better mention the KVM_CAP_MAX_VCPUS defined in XXX patch in the comments.

This already exists as KVM api and documented in Documentation/virt/kvm/api.rst
to get the possible maximum number of vcpus.
This patch make it settable.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>