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AJvYcCXeGM3BUZ/Wezoimn/32P2Zh+myZ4gm09YpjNQBZugy+5d930/OTaNf8KMwnP0OcC4SMzVgb2lqvnbf5l0=@vger.kernel.org X-Gm-Message-State: AOJu0Yw/BgXlmXXzI92wlc/hlDoOiO/5Y2Dz0l+yjRvNHgSePIYBIPmf U0I6jR2akCslIQ+HPYSJuWOgqqdwPo7mWITgNxRnnR6kkzeIpl2wVvPlv67MrLq6lVFpKBezcUE 33kWviQ== X-Google-Smtp-Source: AGHT+IEAgn6mOFzpsqVl9r6+YOxIGAp0ixzr0nLW9znp+DUdsWzttRPnaKMYiSVLJxnM6GKQCDmm2skU950= X-Received: from pjbpw14.prod.google.com ([2002:a17:90b:278e:b0:311:df47:4773]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3807:b0:312:639:a058 with SMTP id 98e67ed59e1d1-3120639afe8mr6031771a91.27.1748529077444; Thu, 29 May 2025 07:31:17 -0700 (PDT) Date: Thu, 29 May 2025 07:31:15 -0700 In-Reply-To: <019c1023c26e827dc538f24d885ec9a8530ad4af.camel@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250519232808.2745331-1-seanjc@google.com> <20250519232808.2745331-12-seanjc@google.com> <019c1023c26e827dc538f24d885ec9a8530ad4af.camel@intel.com> Message-ID: Subject: Re: [PATCH 11/15] KVM: x86: Add CONFIG_KVM_IOAPIC to allow disabling in-kernel I/O APIC From: Sean Christopherson To: Kai Huang Cc: "pbonzini@redhat.com" , "vkuznets@redhat.com" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Thu, May 29, 2025, Kai Huang wrote: > On Thu, 2025-05-29 at 23:55 +1200, Kai Huang wrote: > > On Mon, 2025-05-19 at 16:28 -0700, Sean Christopherson wrote: > > > Add a Kconfig to allowing building KVM without support for emulating = an > > ^ > > allow > >=20 > > > I/O APIC, PIC, and PIT, which is desirable for deployments that effec= tively > > > don't support a fully in-kernel IRQ chip, i.e. never expect any VMM t= o > > > create an in-kernel I/O APIC. =C2=A0 > >=20 > > Do you happen to know what developments don't support a full in-kernel = IRQ chip? Google Cloud, for one. I suspect/assume many/most CSPs don't utilize an in= -kernel I/O APIC. > > Do they only support userspace IRQ chip, or not support any IRQ chip at= all? The former, only userspace I/O APIC (and associated devices), though some V= M shapes, e.g. TDX, don't provide an I/O APIC or PIC. > Forgot to ask: >=20 > Since this new Kconfig option is not only for IOAPIC but also includes PI= C and > PIT, is CONFIG_KVM_IRQCHIP a better name? I much prefer IOAPIC, because IRQCHIP is far too ambiguous and confusing, e= .g. just look at KVM's internal APIs, where these: irqchip_in_kernel() irqchip_kernel() are not equivalent. In practice, no modern guest kernel is going to utiliz= e the PIC, and the PIT isn't an IRQ chip, i.e. isn't strictly covered by IRQCHIP = either. So I think/hope the vast majority of users/readers will be able to intuit t= hat CONFIG_KVM_IOAPIC also covers the PIC and PIT.