linux-kernel - Re: [PATCH v1] kvm: x86: implement PV send

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Message-ID: <aHpmzhaU5JNqhp75@google.com>
Date: Fri, 18 Jul 2025 08:22:54 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: Jason Wang <jasowang@...hat.com>, Cindy Lu <lulu@...hat.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, 
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, 
	"Peter Zijlstra (Intel)" <peterz@...radead.org>, "Kirill A. Shutemov" <kas@...nel.org>, "Xin Li (Intel)" <xin@...or.com>, 
	Rik van Riel <riel@...riel.com>, "Ahmed S. Darwish" <darwi@...utronix.de>, 
	"open list:KVM PARAVIRT (KVM/paravirt)" <kvm@...r.kernel.org>, 
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] kvm: x86: implement PV send_IPI method

On Fri, Jul 18, 2025, Chao Gao wrote:
> >> >> >> From: Jason Wang <jasowang@...hat.com>
> >If xAPIC vs. x2APIC is stable when
> >kvm_setup_pv_ipi() runs, maybe key off of that?
> 
> But the guest doesn't know if APICv is enabled or even IPI virtualization
> is enabled.

Oh yeah, duh.  Given that KVM emulates x2APIC irrespective of hardware support,
and that Linux leans heavily towards x2APIC (thanks MMIO stale data!), my vote
is to leave things as they are.