From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4B5DA22A811 for ; Thu, 29 May 2025 14:31:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748529079; cv=none; b=oUZ3SRR/PTBg3EC+04vhsuBJPabAAwKvAsmg32lXt6CV9hfPKvn2So823Jd5oMc4IiYR6HTQJSOAP+yjDKbsS112xM7pD5wlYYuMTQGHoSNQFcMI1alfjj57p4DINYjh2jwB2uyNxGgvhlRbwnvt8XD1MLl1ifElbbwBFUFTGtI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748529079; c=relaxed/simple; bh=s50DIHBvTSTUoNZI5xejr/EgeAPMXXcRhvG3h1nQbS0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=K7KKiPnBKWGmRWYOxU7iZMT3Iae2Jh5BWjhwKbhNHSaE2+vGZ5LSRmqxQiTdsjkNqUTD5Rf15gZjr4TMcFqtjzQm5Xcddbz0M0eK6TAaaJTHhDZtDfP3QvxFykZ/Llx5SRSvYH4k22huJD6A9HcNyHVzQR2P0Y55R0+v3knAGGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=tDJMEU6j; arc=none smtp.client-ip=209.85.215.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="tDJMEU6j" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-b26cdc70befso606013a12.1 for ; Thu, 29 May 2025 07:31:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1748529077; x=1749133877; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=BHYp1ck4xduERScXV3HMu0GhyVe2Ft9tD7XedzHEDSw=; b=tDJMEU6j83l9zIEDY8NnNAWKf85368lxCm6glm79JfAwgH51gadyg9ZQbOHpMxreuG e9e9SW6LD9SLIVZeNGlhbSDD4syY1lCqZr+NMiiDZhx5DF1LMPGF3n35OPtjd6vuVoGd UU1/LD9Bo9gTPQHjFUWcBkWKfkJMQtQzbsOvNUsP3Jhfl9tuybm9p47UriAyAXOtlt9z lP3IFwifz8PeldeHQItULLA1E3+UlofcT1i6Ear6iMwRtccrgldiCpVGTY68AFvB35LZ Aj+KG30QkZCItVcIEmoqA0gCZJGvzb+a5816M9tlWgeB3tYQSIQq2rtmmEoVkEPGe3hV +bag== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1748529077; x=1749133877; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=BHYp1ck4xduERScXV3HMu0GhyVe2Ft9tD7XedzHEDSw=; b=OoHJpXvfcqr6y95TauTTWD7iuEXxB188AUx8yLzqbvU/7NZLFGmGewohbPY6VWIUFZ E13QaknyUmoWCRFxL1sMG9mXGJ08wXZLWxx+UdR5N8VGUAi+Cta92VuWUlV1ll13093j A+RBmkx6HW9IlXbhI7ReDayOESb1EiDFRfOM3+qXU1YmGo1BAWM9yIT0tkWHKOmmpfq6 eU54waG8aF7onm1UGOJ0225/av0m0KP62Gg55ycEchdG4xSOcNHssCb6Uz1uHc8D7BUJ 9GLpQs2lIpovfg0vSQozESJQwknBlnBiL1E0+wgfAMAG9iYvY8ugYxLCWuUHJwo3Ox1k k8uQ== X-Forwarded-Encrypted: i=1; AJvYcCUaD1LphPLL+3yW1ZPKUf2cVTZq5EvtnWkEGDSgFkqVYNiFURAGhpbh+6t0ZfzJlRCFgeM=@vger.kernel.org X-Gm-Message-State: AOJu0Ywfeaz4lO7DGln6wQ+yYpJtbYrf9Ds0TPEe6wgoy0hiumDMW8xP mGR5Xmp5tRwRRGMFJxpaj4jVfA1EkQ/W7pkxH7lMjHantmG9b2qRmHWWfPPX20Yo8bPRmZs8WW/ FqGCztA== 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: kvm@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.