linux-kernel - Re: [PATCH 02/11] KVM: VMX: Handle APIC-write offset wrangling in VMX code

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Date:   Tue, 15 Feb 2022 10:22:23 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Zeng Guang <guang.zeng@...el.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH 02/11] KVM: VMX: Handle APIC-write offset wrangling in
 VMX code

>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -5302,9 +5302,16 @@ static int handle_apic_eoi_induced(struct kvm_vcpu *vcpu)
> static int handle_apic_write(struct kvm_vcpu *vcpu)
> {
> 	unsigned long exit_qualification = vmx_get_exit_qual(vcpu);
>-	u32 offset = exit_qualification & 0xfff;
> 
>-	/* APIC-write VM exit is trap-like and thus no need to adjust IP */
>+	/*
>+	 * APIC-write VM-Exit is trap-like, KVM doesn't need to advance RIP and
>+	 * hardware has done any necessary aliasing, offset adjustments, etc...
>+	 * for the access.  I.e. the correct value has already been  written to
>+	 * the vAPIC page for the correct 16-byte chunk.  KVM needs only to
>+	 * retrieve the register value and emulate the access.
>+	 */
>+	u32 offset = exit_qualification & 0xff0;

Can we take this opportunity to remove offset/exit_qualification?
They are used just once.

>+
> 	kvm_apic_write_nodecode(vcpu, offset);
> 	return 1;
> }
>-- 
>2.35.0.263.gb82422642f-goog
>