linux-kernel - Re: [PATCH 09/11] KVM: x86: Treat x2APIC's ICR as a 64-bit register, not two 32-bit regs

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Date:   Tue, 15 Feb 2022 11:27:13 +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 09/11] KVM: x86: Treat x2APIC's ICR as a 64-bit register,
 not two 32-bit regs

> 	case APIC_SELF_IPI:
>-		if (apic_x2apic_mode(apic)) {
>-			kvm_lapic_reg_write(apic, APIC_ICR,
>-					    APIC_DEST_SELF | (val & APIC_VECTOR_MASK));
>-		} else
>+		if (apic_x2apic_mode(apic))
>+			kvm_x2apic_icr_write(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK));
>+		else

The original code looks incorrect. Emulating writes to SELF_IPI by writes to
ICR has an unwanted side-effect: the value of ICR in vAPIC page gets changed.

It is better to use kvm_apic_send_ipi() directly.