linux-kernel - Re: [PATCH v10 017/108] KVM: TDX: Refuse to unplug the last cpu on the package

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Date:   Wed, 2 Nov 2022 19:01:20 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Binbin Wu <binbin.wu@...ux.intel.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>
Subject: Re: [PATCH v10 017/108] KVM: TDX: Refuse to unplug the last cpu on
 the package

On Wed, Nov 02, 2022 at 04:06:20PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 4b22196cb12c..25c30c8c2d9b 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12337,16 +12337,23 @@ int kvm_arch_online_cpu(unsigned int cpu, int usage_count)
> >   int kvm_arch_offline_cpu(unsigned int cpu, int usage_count)
> >   {
> > -	if (usage_count) {
> > -		/*
> > -		 * arch callback kvm_arch_hardware_disable() assumes that
> > -		 * preemption is disabled for historical reason.  Disable
> > -		 * preemption until all arch callbacks are fixed.
> > -		 */
> > -		preempt_disable();
> > -		hardware_disable(NULL);
> > -		preempt_enable();
> > -	}
> > +	int ret;
> > +
> > +	if (!usage_count)
> > +		return 0;
> > +
> > +	ret = static_call(kvm_x86_offline_cpu)();
> 
> Use static_call_cond instead?
> Seems the new interface for x86 is only implemented for Intel.

Not needed because KVM_X86_OP_OPTIONAL_RET0(offline_cpu) is used.

Please remember
#define KVM_X86_OP_OPTIONAL_RET0(func) \
        static_call_update(kvm_x86_##func, (void *)kvm_x86_ops.func ? : \
                                           (void *)__static_call_return0);
Thanks,
-- 
Isaku Yamahata <isaku.yamahata@...il.com>