linux-kernel - Re: [PATCH 3/4] KVM/VMX: Invoke NMI non-IST entry instead of IST entry

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Message-ID: <87eeenk2l5.ffs@nanos.tec.linutronix.de>
Date:   Mon, 03 May 2021 22:02:46 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Uros Bizjak <ubizjak@...il.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 3/4] KVM/VMX: Invoke NMI non-IST entry instead of IST entry

On Tue, Apr 27 2021 at 07:09, Lai Jiangshan wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index bcbf0d2139e9..96e59d912637 100644
> --- 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>
> @@ -6416,8 +6417,11 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
>  	else if (is_machine_check(intr_info))
>  		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);
> +	else if (is_nmi(intr_info)) {

Lacks curly braces for all of the above conditions according to coding style.

> +		kvm_before_interrupt(&vmx->vcpu);
> +		vmx_do_interrupt_nmi_irqoff((unsigned long)asm_noist_exc_nmi);
> +		kvm_after_interrupt(&vmx->vcpu);
> +	}

but this and the next patch are not really needed. The below avoids the
extra kvm_before/after() dance in both places. Hmm?

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)