linux-kernel - Re: [PATCH v3 16/27] KVM: VMX: Virtualize FRED nested exception tracking

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Message-ID: <ZxnoE6ltLawgPHdZ@intel.com>
Date: Thu, 24 Oct 2024 14:24:19 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Xin Li (Intel)" <xin@...or.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<corbet@....net>, <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<luto@...nel.org>, <peterz@...radead.org>, <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v3 16/27] KVM: VMX: Virtualize FRED nested exception
 tracking

>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>index b9b82aaea9a3..3830084b569b 100644
>--- a/arch/x86/include/asm/kvm_host.h
>+++ b/arch/x86/include/asm/kvm_host.h
>@@ -736,6 +736,7 @@ struct kvm_queued_exception {
> 	u32 error_code;
> 	unsigned long payload;
> 	bool has_payload;
>+	bool nested;
> 	u64 event_data;

how "nested" is migrated in live migration?

> };

[..]

> 
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index d81144bd648f..03f42b218554 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -1910,8 +1910,11 @@ void vmx_inject_exception(struct kvm_vcpu *vcpu)
> 		vmcs_write32(VM_ENTRY_INSTRUCTION_LEN,
> 			     vmx->vcpu.arch.event_exit_inst_len);
> 		intr_info |= INTR_TYPE_SOFT_EXCEPTION;
>-	} else
>+	} else {
> 		intr_info |= INTR_TYPE_HARD_EXCEPTION;
>+		if (ex->nested)
>+			intr_info |= INTR_INFO_NESTED_EXCEPTION_MASK;

how about moving the is_fred_enable() check from kvm_multiple_exception() to here? i.e.,

		if (ex->nested && is_fred_enabled(vcpu))
			intr_info |= INTR_INFO_NESTED_EXCEPTION_MASK;

It is slightly clearer because FRED details don't bleed into kvm_multiple_exception().

>+	}
> 
> 	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
> 
>@@ -7290,6 +7293,7 @@ static void __vmx_complete_interrupts(struct kvm_vcpu *vcpu,
> 		kvm_requeue_exception(vcpu, vector,
> 				      idt_vectoring_info & VECTORING_INFO_DELIVER_CODE_MASK,
> 				      error_code,
>+				      idt_vectoring_info & VECTORING_INFO_NESTED_EXCEPTION_MASK,
> 				      event_data);
> 		break;
> 	}
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 7a55c1eb5297..8546629166e9 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -874,6 +874,11 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu, unsigned int nr,
> 		vcpu->arch.exception.pending = true;
> 		vcpu->arch.exception.injected = false;
> 
>+		vcpu->arch.exception.nested = vcpu->arch.exception.nested ||
>+					      (is_fred_enabled(vcpu) &&
>+					       (vcpu->arch.nmi_injected ||
>+					        vcpu->arch.interrupt.injected));
>+
> 		vcpu->arch.exception.has_error_code = has_error;
> 		vcpu->arch.exception.vector = nr;
> 		vcpu->arch.exception.error_code = error_code;
>@@ -903,8 +908,13 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu, unsigned int nr,
> 		vcpu->arch.exception.injected = false;
> 		vcpu->arch.exception.pending = false;
> 
>+		/* #DF is NOT a nested event, per its definition. */
>+		vcpu->arch.exception.nested = false;
>+
> 		kvm_queue_exception_e(vcpu, DF_VECTOR, 0);
> 	} else {
>+		vcpu->arch.exception.nested = is_fred_enabled(vcpu);
>+
> 		/* replace previous exception with a new one in a hope
> 		   that instruction re-execution will regenerate lost
> 		   exception */