linux-kernel - Re: [PATCH v14 004/113] KVM: TDX: Initialize the TDX module when loading the KVM intel kernel module

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Date:   Tue, 30 May 2023 10:14:15 -0700
From:   Sean Christopherson <seanjc@...gle.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,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>, chen.bo@...el.com
Subject: Re: [PATCH v14 004/113] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module

On Tue, May 30, 2023, Zhi Wang wrote:
> On Sun, 28 May 2023 21:18:46 -0700 isaku.yamahata@...el.com wrote:
> > +	/* tdx_enable() in tdx_module_setup() requires cpus lock. */
> > +	cpus_read_lock();
> > +	on_each_cpu(vmx_tdx_on, &err, true);	/* TDX requires vmxon. */
> > +	r = atomic_read(&err);
> > +	if (!r)
> > +		r = tdx_module_setup();
> > +	on_each_cpu(vmx_off, NULL, true);
> 
> Out of curiosity, why VMX has to be turned off after tdx_module_setup()?

KVM has historically enabled VMX if and only if KVM has active VMs.  Whether or
not it still makes sense to do dynamic enabling is debatable, but that's a
discussion for another day.