From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753326AbcGDIPH (ORCPT <rfc822;w@1wt.eu>);
	Mon, 4 Jul 2016 04:15:07 -0400
Received: from mail-wm0-f67.google.com ([74.125.82.67]:35534 "EHLO
	mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753054AbcGDIPE (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 4 Jul 2016 04:15:04 -0400
Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed
To: Xiao Guangrong <guangrong.xiao@linux.intel.com>, Neo Jia <cjia@nvidia.com>
References: <1467291711-3230-1-git-send-email-pbonzini@redhat.com>
 <577A049A.4000402@linux.intel.com> <20160704070314.GA13291@nvidia.com>
 <577A123F.1060909@linux.intel.com>
 <8ff54c7b-2e64-4503-03f6-1a858d9d5746@redhat.com>
 <577A1765.6080606@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Kirti Wankhede <kwankhede@nvidia.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <b11e9316-4460-6502-0e1c-74555ff84d6a@redhat.com>
Date: Mon, 4 Jul 2016 10:14:56 +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: <577A1765.6080606@linux.intel.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On 04/07/2016 09:59, Xiao Guangrong wrote:
> 
>> 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.
> 
> Well,  it's little strange as you always try to get refcont
> for a PFNMAP region without MIXEDMAP which indicates all the memory
> in this region is no 'struct page' backend.

Fair enough, I can modify the comment.

	/*
	 * In case the VMA has VM_MIXEDMAP set, whoever called remap_pfn_range
	 * is also going to call e.g. unmap_mapping_range before the underlying
	 * non-reserved pages are freed, which will then call our MMU notifier.
	 * We still have to get a reference here to the page, because the callers
	 * of *hva_to_pfn* and *gfn_to_pfn* ultimately end up doing a
	 * kvm_release_pfn_clean on the returned pfn.  If the pfn is
	 * reserved, the kvm_get_pfn/kvm_release_pfn_clean pair will simply
	 * do nothing.
	 */

Paolo

> But it works as kvm_{get, release}_* have already been aware of
> reserved_pfn, so i am okay with it......