From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8ADD37E2FB for ; Wed, 8 Jul 2026 13:39:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783517959; cv=none; b=uCxykiR9JnMyI/J3ZaN7yTIzH8SVhtSITOxO5zGK0n3bXpWshhsEQFnD5r2r+PBvoC6GYWC7EQNl68QOThIL2oBwNc0F/5Sos3DgjFwhJBU+8gZ+3VNAsV01UDO66mTDnpHI7L04ZuXzp2+P6RioWEZV1WQj9eVmvFyTFIzFrT0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783517959; c=relaxed/simple; bh=/0g+Y4wPFerm9mXGe154aQarap2+uauds1ZHfE+SLQc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=UxC/BpdBiVCqEG3vQ+2/RjRFAOietFrvetr2VjE4jMK6F1wSPeKo+iymjmGNXWfDc/pUPtf+4eYiFh6/Xt8XNO4FBeFnQLcfjO4RQqS+cOWrxg/apfIwcSfPk9aJN8NZFcwUuMCury3zRpsb91FW1QauwmzxicEuSGGzFVJPbjk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=H8w2Wv3j; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="H8w2Wv3j" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783517956; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=ECVWxNUMUUQjHTObpd3YI7AQD/uZ8AjllXMw0PpKKdE=; b=H8w2Wv3jgzVvf6oG1iZ2uwA9Z0JwJ2IPFTDo/jcgrwSvKPjId+t1WndwteUH5EZ1C6t7tL hDcSbUGC610PBY67LLB3MCz+mJJACd6DiHua8hbvpJefFfmfp1YRYzGiDans+tRUKan5RZ EEeu5MgSBPR5zV2a0fXa2XQGAyzadU4= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-649-VvKfb93-PWWDpygkYNfy2Q-1; Wed, 08 Jul 2026 09:39:13 -0400 X-MC-Unique: VvKfb93-PWWDpygkYNfy2Q-1 X-Mimecast-MFC-AGG-ID: VvKfb93-PWWDpygkYNfy2Q_1783517951 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id ED33018005B1; Wed, 8 Jul 2026 13:39:10 +0000 (UTC) Received: from work.fritz.box (unknown [10.44.49.159]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 71BA03000C13; Wed, 8 Jul 2026 13:39:08 +0000 (UTC) From: Tim Wiederhake To: Sean Christopherson , Jonathan Corbet , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Shuah Khan Cc: Tim Wiederhake Subject: [PATCH v2 0/2] KVM: x86: Document APIC base memory hole constraint Date: Wed, 8 Jul 2026 15:38:53 +0200 Message-ID: <20260708133856.302151-1-twiederh@redhat.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 When virtual APIC access acceleration is enabled on x86 (APICv on Intel, AVIC on AMD), vcpu creation installs a private memory slot at the default APIC base address (0xfee00000). If user space maps a memory region covering that address, vcpu creation fails with -EEXIST. This is not documented and very puzzling when it happens. This series documents two undocumented constraints: 1/2 KVM_CREATE_IRQCHIP must precede vcpu creation 2/2 APIC base address memory hole when APIC acceleration is enabled Thanks to Sean Christopherson for the thorough review of v1. Changes since v1: - Dropped enforcement patches (3/4, 4/4) per review feedback. - Patch 1/2: Reworded to avoid implying that KVM_CREATE_IRQCHIP is mandatory. - Patch 2/2: Reworded to reflect that the APIC access page is not installed in every case. Added note about KVM_CAP_SPLIT_IRQCHIP having the same constraint. v1: https://lore.kernel.org/kvm/20260706092021.3625908-2-twiederh@redhat.com/ Tim Wiederhake (2): KVM: x86: Document that KVM_CREATE_IRQCHIP must precede vcpu creation KVM: x86: Document APIC base address constraint for in-kernel irqchip Documentation/virt/kvm/api.rst | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) -- 2.52.0