linux-kernel - Re: [PATCH v8 33/33] KVM: x86/vmx: refactor VMX_DO_EVENT

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Date:   Tue, 11 Apr 2023 11:34:23 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Xin3 Li <xin3.li@...el.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        "jiangshanlai@...il.com" <jiangshanlai@...il.com>,
        Shan Kang <shan.kang@...el.com>
Subject: Re: [PATCH v8 33/33] KVM: x86/vmx: refactor VMX_DO_EVENT_IRQOFF to
 generate FRED stack frames

On Tue, Apr 11, 2023, Xin3 Li wrote:
> > 
> >  	kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ);
> > -	vmx_do_interrupt_irqoff(gate_offset(desc));
> > +	if (cpu_feature_enabled(X86_FEATURE_FRED))
> > +		vmx_do_fred_interrupt_irqoff(vector);
> > +	else
> > +		vmx_do_interrupt_irqoff(gate_offset((gate_desc *)host_idt_base
> 
> 
> external_interrupt() is always available on x86_64, even when CONFIG_X86_FRED
> is not defined. I prefer to always call external_interrupt() on x86_64 for IRQ
> handling, which avoids re-entering noinstr code. how do you think? Too
> aggressive?

I think it's completely orthogonal to FRED enabling.  If you or anyone else wants
to convert the non-FRED handling to external_interrupt(), then do so after FRED
lands, or at the very least in a separate patch after enabling FRED in KVM.