From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3tg4gF6pXxzDsyf for ; Fri, 16 Dec 2016 20:26:01 +1100 (AEDT) Subject: Re: [PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for HPT resizing To: David Gibson , paulus@samba.org References: <20161215055404.29351-1-david@gibson.dropbear.id.au> <20161215055404.29351-2-david@gibson.dropbear.id.au> Cc: michael@ellerman.id.au, benh@kernel.crashing.org, sjitindarsingh@gmail.com, lvivier@redhat.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org From: Thomas Huth Message-ID: <25bcced1-4903-2cf7-6a56-14c3ced5cd28@redhat.com> Date: Fri, 16 Dec 2016 10:25:55 +0100 MIME-Version: 1.0 In-Reply-To: <20161215055404.29351-2-david@gibson.dropbear.id.au> Content-Type: text/plain; charset=utf-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 15.12.2016 06:53, David Gibson wrote: > This adds a new powerpc-specific KVM_CAP_SPAPR_RESIZE_HPT capability to > advertise whether KVM is capable of handling the PAPR extensions for > resizing the hashed page table during guest runtime. > > At present, HPT resizing is possible with KVM PR without kernel > modification, since the HPT is managed within qemu. It's not possible yet > with KVM HV, because the HPT is managed by KVM. At present, qemu has to > use other capabilities which (by accident) reveal whether PR or HV is in > use to know if it can advertise HPT resizing capability to the guest. > > To avoid ambiguity with existing kernels, the encoding is a bit odd. > 0 means "unknown" since that's what previous kernels will return > 1 means "HPT resize possible if available if and only if the HPT is allocated in > userspace, rather than in the kernel". Userspace can check > KVM_CAP_PPC_ALLOC_HTAB to determine if that's the case. In practice > this will give the same results as userspace's fallback check. > 2 will mean "HPT resize available and implemented via ioctl()s > KVM_PPC_RESIZE_HPT_PREPARE and KVM_PPC_RESIZE_HPT_COMMIT" This encoding IMHO clearly needs some proper documentation in Documentation/virtual/kvm/api.txt ... and maybe also some dedicated #defines in an uapi header file. Thomas