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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id m191sm11505013pga.88.2021.06.08.09.35.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Jun 2021 09:35:47 -0700 (PDT) Date: Tue, 8 Jun 2021 16:35:43 +0000 From: Sean Christopherson To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH v2 3/3] KVM: X86: Let's harden the ipi fastpath condition edge-trigger mode Message-ID: References: <1623050385-100988-1-git-send-email-wanpengli@tencent.com> <1623050385-100988-3-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1623050385-100988-3-git-send-email-wanpengli@tencent.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 07, 2021, Wanpeng Li wrote: > From: Wanpeng Li > > Let's harden the ipi fastpath condition edge-trigger mode. Can you elaborate on the motivation for this patch? Intel's SDM states that the trigger mode is ignored for all IPIs except INIT, and even clarifies that the local xAPIC will override the bit and send the IPI as edge-triggered. AMD's APM on the other hand explicitly lists level-triggered Fixed IPIs as a valid ICR combination. Regardless of which of the two conflicting specs we want KVM to emulate (which is currently AMD), I don't see why the fastpath code should care, as I can't find anything in the kvm_apic_send_ipi() path that would go awry if it's called from the fastpath for a level-triggered IPI. Related side topic, anyone happen to know if KVM (and Qemu's) emulation of IPIs intentionally follows AMD instead of Intel? I suspect it's unintentional, especially since KVM's initial xAPIC emulation came from Intel. Not that it's likely to matter, but allowing level-triggered IPIs is bizarre, e.g. getting an EOI sent to the right I/O APIC at the right time via a level-triggered IPI seems extremely convoluted. > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/x86.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index b594275..dbd3e9d 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1922,6 +1922,7 @@ static int handle_fastpath_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u64 data > return 1; > > if (((data & APIC_SHORT_MASK) == APIC_DEST_NOSHORT) && > + ((data & APIC_INT_LEVELTRIG) == 0) && > ((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) && > ((data & APIC_MODE_MASK) == APIC_DM_FIXED) && > ((u32)(data >> 32) != X2APIC_BROADCAST)) { > -- > 2.7.4 >