linux-kernel - Re: [PATCH v19 023/130] KVM: TDX: Initialize the TDX module when loading the KVM intel kernel module

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Date: Fri, 22 Mar 2024 11:01:41 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>,
	"Zhang, Tina" <tina.zhang@...el.com>,
	"isaku.yamahata@...ux.intel.com" <isaku.yamahata@...ux.intel.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>,
	"Yuan, Hang" <hang.yuan@...el.com>, "Chen, Bo2" <chen.bo@...el.com>,
	"sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v19 023/130] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module

On Thu, Mar 21, 2024 at 12:39:34PM +0000,
"Huang, Kai" <kai.huang@...el.com> wrote:

> On Fri, 2024-03-15 at 16:25 -0700, Isaku Yamahata wrote:
> > > > > How about if there are some LPs that are offline.
> > > > > In tdx_hardware_setup(), only online LPs are initialed for TDX, right?
> > > > Correct.
> > > > 
> > > > 
> > > > > Then when an offline LP becoming online, it doesn't have a chance to call
> > > > > tdx_cpu_enable()?
> > > > KVM registers kvm_online/offline_cpu() @ kvm_main.c as cpu hotplug callbacks.
> > > > Eventually x86 kvm hardware_enable() is called on online/offline event.
> > > 
> > > Yes, hardware_enable() will be called when online,
> > > but  hardware_enable() now is vmx_hardware_enable() right?
> > > It doens't call tdx_cpu_enable() during the online path.
> > 
> > TDX module requires TDH.SYS.LP.INIT() on all logical processors(LPs).  If we
> > successfully initialized TDX module, we don't need further action for TDX on cpu
> > online/offline.
> > 
> > If some of LPs are not online when loading kvm_intel.ko, KVM fails to initialize
> > TDX module. TDX support is disabled.  We don't bother to attempt it.  Leave it
> > to the admin of the machine.
> 
> No.  We have relaxed this.  Now the TDX module can be initialized on a subset of
> all logical cpus, with arbitrary number of cpus being offline.  
> 
> Those cpus can become online after module initialization, and TDH.SYS.LP.INIT on
> them won't fail.

Ah, you're right. So we need to call tdx_cpu_enable() on online.  For offline,
KVM has to do nothing.  It's another story to shutdown TDX module.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>