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Date:   Tue, 11 Apr 2023 11:34:23 -0700
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Message-ID: <ZDWoL6o5LYgWP14y@google.com>
Subject: Re: [PATCH v8 33/33] KVM: x86/vmx: refactor VMX_DO_EVENT_IRQOFF to
 generate FRED stack frames
From:   Sean Christopherson <seanjc@google.com>
To:     Xin3 Li <xin3.li@intel.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        "jiangshanlai@gmail.com" <jiangshanlai@gmail.com>,
        Shan Kang <shan.kang@intel.com>
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Precedence: bulk

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.