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Subject: Re: [PATCH 3/4] KVM/VMX: Invoke NMI non-IST entry instead of IST
 entry
To:     Thomas Gleixner <tglx@linutronix.de>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Sean Christopherson <seanjc@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andi Kleen <ak@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Uros Bizjak <ubizjak@gmail.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>
References: <20210426230949.3561-1-jiangshanlai@gmail.com>
 <20210426230949.3561-4-jiangshanlai@gmail.com>
 <87eeenk2l5.ffs@nanos.tec.linutronix.de>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <baa499a7-2b63-2970-04a6-e2c68796adc7@redhat.com>
Date:   Tue, 4 May 2021 10:10:42 +0200
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On 03/05/21 22:02, Thomas Gleixner wrote:
> but this and the next patch are not really needed. The below avoids the
> extra kvm_before/after() dance in both places. Hmm?

Sure, that's good as well.

Paolo

> Thanks,
> 
>          tglx
> ---
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -526,6 +526,10 @@ DEFINE_IDTENTRY_RAW(exc_nmi)
>   
>   DEFINE_IDTENTRY_RAW_ALIAS(exc_nmi, exc_nmi_noist);
>   
> +#if IS_MODULE(CONFIG_KVM_INTEL)
> +EXPORT_SYMBOL_GPL(asm_exc_nmi_noist);
> +#endif
> +
>   void stop_nmi(void)
>   {
>   	ignore_nmis++;
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -36,6 +36,7 @@
>   #include <asm/debugreg.h>
>   #include <asm/desc.h>
>   #include <asm/fpu/internal.h>
> +#include <asm/idtentry.h>
>   #include <asm/io.h>
>   #include <asm/irq_remapping.h>
>   #include <asm/kexec.h>
> @@ -6395,18 +6396,17 @@ static void vmx_apicv_post_state_restore
>   
>   void vmx_do_interrupt_nmi_irqoff(unsigned long entry);
>   
> -static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu, u32 intr_info)
> +static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu,
> +					unsigned long entry)
>   {
> -	unsigned int vector = intr_info & INTR_INFO_VECTOR_MASK;
> -	gate_desc *desc = (gate_desc *)host_idt_base + vector;
> -
>   	kvm_before_interrupt(vcpu);
> -	vmx_do_interrupt_nmi_irqoff(gate_offset(desc));
> +	vmx_do_interrupt_nmi_irqoff(entry);
>   	kvm_after_interrupt(vcpu);
>   }
>   
>   static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
>   {
> +	const unsigned long nmi_entry = (unsigned long)asm_exc_nmi_noist;
>   	u32 intr_info = vmx_get_intr_info(&vmx->vcpu);
>   
>   	/* if exit due to PF check for async PF */
> @@ -6417,18 +6417,20 @@ static void handle_exception_nmi_irqoff(
>   		kvm_machine_check();
>   	/* We need to handle NMIs before interrupts are enabled */
>   	else if (is_nmi(intr_info))
> -		handle_interrupt_nmi_irqoff(&vmx->vcpu, intr_info);
> +		handle_interrupt_nmi_irqoff(&vmx->vcpu, nmi_entry);
>   }
>   
>   static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
>   {
>   	u32 intr_info = vmx_get_intr_info(vcpu);
> +	unsigned int vector = intr_info & INTR_INFO_VECTOR_MASK;
> +	gate_desc *desc = (gate_desc *)host_idt_base + vector;
>   
>   	if (WARN_ONCE(!is_external_intr(intr_info),
>   	    "KVM: unexpected VM-Exit interrupt info: 0x%x", intr_info))
>   		return;
>   
> -	handle_interrupt_nmi_irqoff(vcpu, intr_info);
> +	handle_interrupt_nmi_irqoff(vcpu, gate_offset(desc));
>   }
>   
>   static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu)