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Message-ID: <20230329233258.GC1108448@ls.amr.corp.intel.com>
Date: Wed, 29 Mar 2023 16:32:58 -0700
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>,
Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCH v13 018/113] KVM: x86, tdx: Make KVM_CAP_MAX_VCPUS
backend specific
On Sat, Mar 25, 2023 at 08:13:26PM +0200,
Zhi Wang <zhi.wang.linux@...il.com> wrote:
> On Sun, 12 Mar 2023 10:55:42 -0700
> isaku.yamahata@...el.com wrote:
>
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> >
> > TDX has its own limitation on the maximum number of vcpus that the guest
> > can accommodate. Allow x86 kvm backend to implement its own KVM_ENABLE_CAP
> > handler and implement TDX backend for KVM_CAP_MAX_VCPUS. user space VMM,
> > e.g. qemu, can specify its value instead of KVM_MAX_VCPUS.
> >
>
> I think enabling the cap here is actually "configuring the cap". KVM_CAP_MAX
> _VCPUS is actually always enabled whether userspace enables it or not. It
> would be nice to configure of the max VCPUS in kvm_arch_vm_ioctl() where
> routines of configuring a VM should belong. E.g. KVM_SET_MAX_VCPUS.
I'm not sure I understand your point. Although KVM_ENABLE_CAP sounds like
only on/off feature, but it isn't. It's also used to set parameters. For
example, KVM_CAP_MAX_VCPU_ID.
KVM_SET_XXX is for run time feature. But the maxium number of vcpus is not
runtime changable. Set it at vm creation.
--
Isaku Yamahata <isaku.yamahata@...il.com>
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