Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751726AbaFEMam (ORCPT ); Thu, 5 Jun 2014 08:30:42 -0400 Received: from gate.crashing.org ([63.228.1.57]:56200 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751677AbaFEMak (ORCPT ); Thu, 5 Jun 2014 08:30:40 -0400 Message-ID: <1401971411.3247.132.camel@pasglop> Subject: Re: [PATCH 3/3] PPC: KVM: Add support for 64bit TCE windows From: Benjamin Herrenschmidt To: Alexander Graf Cc: Alexey Kardashevskiy , linuxppc-dev@lists.ozlabs.org, Paul Mackerras , Gleb Natapov , Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org Date: Thu, 05 Jun 2014 22:30:11 +1000 In-Reply-To: <53905ADB.8000100@suse.de> References: <1401953144-19186-1-git-send-email-aik@ozlabs.ru> <1401953144-19186-4-git-send-email-aik@ozlabs.ru> <1401953908.3247.121.camel@pasglop> <539037DB.5080706@ozlabs.ru> <1401964037.3247.129.camel@pasglop> <53905ADB.8000100@suse.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-06-05 at 13:56 +0200, Alexander Graf wrote: > What if we ask user space to give us a pointer to user space allocated > memory along with the TCE registration? We would still ask user space to > only use the returned fd for TCE modifications, but would have some > nicely swappable memory we can store the TCE entries in. That isn't going to work terribly well for VFIO :-) But yes, for emulated devices, we could improve things a bit, including for the 32-bit TCE tables. For emulated, the real mode path could walk the page tables and fallback to virtual mode & get_user if the page isn't present, thus operating directly on qemu memory TCE tables instead of the current pinned stuff. However that has a cost in performance, but since that's really only used for emulated devices and PAPR VIOs, it might not be a huge issue. But for VFIO we don't have much choice, we need to create something the HW can access. > In fact, the code as is today can allocate an arbitrary amount of pinned > kernel memory from within user space without any checks. Right. We should at least account it in the locked limit. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/