From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753243AbcGDHtD (ORCPT ); Mon, 4 Jul 2016 03:49:03 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:34865 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752707AbcGDHtA (ORCPT ); Mon, 4 Jul 2016 03:49:00 -0400 Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed To: Xiao Guangrong , Neo Jia References: <1467291711-3230-1-git-send-email-pbonzini@redhat.com> <577A049A.4000402@linux.intel.com> <20160704070314.GA13291@nvidia.com> <577A123F.1060909@linux.intel.com> Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kirti Wankhede , Andrea Arcangeli , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= From: Paolo Bonzini Message-ID: <8ff54c7b-2e64-4503-03f6-1a858d9d5746@redhat.com> Date: Mon, 4 Jul 2016 09:48:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <577A123F.1060909@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/07/2016 09:37, Xiao Guangrong wrote: >>> >> >> It actually is a portion of the physical mmio which is set by vfio mmap. > > So i do not think we need to care its refcount, i,e, we can consider it > as reserved_pfn, > Paolo? nVidia provided me (offlist) with a simple patch that modified VFIO to exhibit the problem, and it didn't use reserved PFNs. This is why the commit message for the patch is not entirely accurate. But apart from this, it's much more obvious to consider the refcount. The x86 MMU code doesn't care if the page is reserved or not; mmu_set_spte does a kvm_release_pfn_clean, hence it makes sense for hva_to_pfn_remapped to try doing a get_page (via kvm_get_pfn) after invoking the fault handler, just like the get_user_pages family of function does. Paolo