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AJvYcCUR/kqqNxmrRYIdKD4oUmRl8MF822r3GFk8xcmorJbFrfLYvTKGmW+oh2qTH2PV6MoLrnJQVq4=@vger.kernel.org X-Gm-Message-State: AOJu0YyAtW9nGrzHIn/+fjXhfTdCk0ox4I+Anf68+jwPp4ghjv7NkIvF mfzkZUBWrdACGukY3HzpP1YwSggccqhzGHQi9mpDq87QKjKoxgbow/sbqeleNWF7gBzfqxyvbbV AAmf7KA== X-Received: from pjuy19.prod.google.com ([2002:a17:90a:d713:b0:34a:b8e4:f1b9]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:e2cc:b0:353:39bd:3ad2 with SMTP id 98e67ed59e1d1-353fecd0958mr1793042a91.5.1769550544803; Tue, 27 Jan 2026 13:49:04 -0800 (PST) Date: Tue, 27 Jan 2026 13:49:03 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260123125657.3384063-1-khushit.shah@nutanix.com> Message-ID: Subject: Re: [PATCH v6] KVM: x86: Add x2APIC "features" to control EOI broadcast suppression From: Sean Christopherson To: David Woodhouse Cc: Khushit Shah , pbonzini@redhat.com, kai.huang@intel.com, mingo@redhat.com, x86@kernel.org, bp@alien8.de, hpa@zytor.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, dave.hansen@linux.intel.com, tglx@linutronix.de, jon@nutanix.com, shaju.abraham@nutanix.com, stable@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Tue, Jan 27, 2026, David Woodhouse wrote: > On Fri, 2026-01-23 at 12:56 +0000, Khushit Shah wrote: > >=20 > > @@ -4931,6 +4933,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm,= long ext) > > =C2=A0 break; > > =C2=A0 case KVM_CAP_X2APIC_API: > > =C2=A0 r =3D KVM_X2APIC_API_VALID_FLAGS; > > + if (kvm && !irqchip_split(kvm)) > > + r &=3D ~KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST; > > =C2=A0 break; > > =C2=A0 case KVM_CAP_NESTED_STATE: > > =C2=A0 r =3D kvm_x86_ops.nested_ops->get_state ? > > @@ -6748,11 +6752,24 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, > > =C2=A0 if (cap->args[0] & ~KVM_X2APIC_API_VALID_FLAGS) > > =C2=A0 break; > > =C2=A0 > > + if ((cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST) && > > + =C2=A0=C2=A0=C2=A0 (cap->args[0] & KVM_X2APIC_DISABLE_SUPPRESS_EOI_B= ROADCAST)) > > + break; > > + > > + if ((cap->args[0] & KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST) && > > + =C2=A0=C2=A0=C2=A0 !irqchip_split(kvm)) > > + break; > > + > > =C2=A0 if (cap->args[0] & KVM_X2APIC_API_USE_32BIT_IDS) >=20 > Is it possible to set KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST and > *then* create the in-kernel I/O APIC? Nope, we should be good on that front, kvm->arch.irqchip_mode can't be chan= ged once its set. I.e. the irqchip_split() check could get a false negative if= it's racing with KVM_CREATE_IRQCHIP, but it can't get a false positive and thus incorrectly allow KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST.