linux-kernel - Re: [RFC PATCH v5 008/104] KVM: TDX: Add a function to initialize TDX module

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Date:   Mon, 14 Mar 2022 12:45:13 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 008/104] KVM: TDX: Add a function to initialize
 TDX module

On Sun, Mar 13, 2022 at 03:03:40PM +0100,
Paolo Bonzini <pbonzini@...hat.com> wrote:

> On 3/4/22 20:48, isaku.yamahata@...el.com wrote:
> > +
> > +	if (!tdx_module_initialized) {
> > +		if (enable_tdx) {
> > +			ret = __tdx_module_setup();
> > +			if (ret)
> > +				enable_tdx = false;
> 
> "enable_tdx = false" isn't great to do only when a VM is created.  Does it
> make sense to anticipate this to the point when the kvm_intel.ko module is
> loaded?

It's possible.  I have the following two reasons to chose to defer TDX module
initialization until creating first TD.  Given those reasons, do you still want
the initialization at loading kvm_intel.ko module?  If yes, I'll change it.

- memory over head: The initialization of TDX module requires to allocate
physically contiguous memory whose size is about 0.43% of the system memory.
If user don't use TD, it will be wasted.

- VMXON on all pCPUs: The TDX module initialization requires to enable VMX
(VMXON) on all present pCPUs.  vmx_hardware_enable() which is called on creating
guest does it.  It naturally fits with the TDX module initialization at creating
first TD.  I wanted to avoid code to enable VMXON on loading the kvm_intel.ko.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>