linux-kernel - Re: [PATCH v13 003/113] KVM: TDX: Initialize the TDX module when loading the KVM intel kernel module

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Date:   Tue, 28 Mar 2023 16:58:39 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "zhi.wang.linux@...il.com" <zhi.wang.linux@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v13 003/113] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module

On Fri, Mar 24, 2023 at 10:41:56AM +0000,
"Huang, Kai" <kai.huang@...el.com> wrote:

> > +static int __init tdx_module_setup(void)
> > +{
> > +	int ret;
> > +
> > +	ret = tdx_enable();
> > +	if (ret) {
> > +		pr_info("Failed to initialize TDX module.\n");
> > +		return ret;
> > +	}
> > +
> > +	pr_info("TDX is supported.\n");
> 
> Both pr_info()s are not required, because tdx_enable() internally prints them.

Ok, will drop this line.


> >  #endif /* __KVM_X86_VMX_X86_OPS_H */
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 2125fcaa3973..b264012a8478 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -9435,6 +9435,16 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> >  
> >  	kvm_init_pmu_capability(ops->pmu_ops);
> >  
> > +	/*
> > +	 * TDX requires those methods to enable VMXON by
> > +	 * kvm_hardware_enable/disable_all()
> > +	 */
> > +	static_call_update(kvm_x86_check_processor_compatibility,
> > +			   ops->runtime_ops->check_processor_compatibility);
> > +	static_call_update(kvm_x86_hardware_enable,
> > +			   ops->runtime_ops->hardware_enable);
> > +	static_call_update(kvm_x86_hardware_disable,
> > +			   ops->runtime_ops->hardware_disable);
> >  	r = ops->hardware_setup();
> >  	if (r != 0)
> >  		goto out_mmu_exit;
> 
> Hmm.. I think this is ugly.  Perhaps we should never do any
> static_call(kvm_x86_xxx)() in hardware_setup(), because hardware_setup() is
> called before kvm_ops_update() and may update vendor's kvm_x86_ops.
> 
> So probably use hardware_enable_all() in hardware_setup() is a bad idea.
> 
> I think we have below options on how to handle:
> 
> 1) Use VMX's kvm_x86_ops directly in tdx_hardware_setup().  For instance,
> something like below:
> 
> int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> {
> 	...
> 
> 	cpus_read_lock();
> 	r = on_each_cpu(vt_x86_ops.hardware_enable, ...);
> 	if (!r)
> 		r = tdx_module_setup();
> 	on_each_cpu(vt_x86_ops.hardware_disable, ...);
> 	cpus_read_unlock();
> 
> 	...
> }
> 
> But this doesn't clean up nicely when there's some particular cpus fail to do
> hardware_enable().  To clean up nicely, we do need additional things similar to
> the hardware_enable_all() code path: a per-cpu variable or a cpumask_t + a
> wrapper of vt_x86_ops->hardware_enable() to track which cpus have done
> hardware_enable() successfully.
> 
> 2) Move those static_call_update() into tdx_hardware_setup() so they are TDX
> code self-contained.  But this would require exposing kvm_x86_ops as symbol,
> which isn't nice either.
> 
> 3) Introduce another kvm_x86_init_ops->hardware_post_setup(), which is called
> after kvm_ops_update().
> 
> Personally, I think 3) perhaps is the most elegant one, but not sure whether
> Sean/Paolo has any opinion.

I think we can simply update the ops before calling hardware_enable() and
clean up ops on failure.


diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 709134e7c12e..42c9b58fd1ef 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9436,20 +9436,15 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 	kvm_init_pmu_capability(ops->pmu_ops);
 
 	/*
-	 * TDX requires those methods to enable VMXON by
-	 * kvm_hardware_enable/disable_all_nolock()
+	 * Because TDX hardware_setup uses x86_ops, update ops before calling
+	 * ops->hardware_setup().
 	 */
-	static_call_update(kvm_x86_check_processor_compatibility,
-			   ops->runtime_ops->check_processor_compatibility);
-	static_call_update(kvm_x86_hardware_enable,
-			   ops->runtime_ops->hardware_enable);
-	static_call_update(kvm_x86_hardware_disable,
-			   ops->runtime_ops->hardware_disable);
+	kvm_ops_update(ops);
 	r = ops->hardware_setup();
-	if (r != 0)
+	if (r != 0) {
+		kvm_x86_ops.hardware_enable = NULL;
 		goto out_mmu_exit;
-
-	kvm_ops_update(ops);
+	}
 
 	for_each_online_cpu(cpu) {
 		smp_call_function_single(cpu, kvm_x86_check_cpu_compat, &r, 1);


-- 
Isaku Yamahata <isaku.yamahata@...il.com>