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 S1753286AbcGDIDU (ORCPT <rfc822;w@1wt.eu>);
	Mon, 4 Jul 2016 04:03:20 -0400
Received: from mga11.intel.com ([192.55.52.93]:1633 "EHLO mga11.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750895AbcGDIDQ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 4 Jul 2016 04:03:16 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.26,573,1459839600"; 
   d="scan'208";a="1015116418"
Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed
To: Paolo Bonzini <pbonzini@redhat.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>
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: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Message-ID: <577A1765.6080606@linux.intel.com>
Date: Mon, 4 Jul 2016 15:59:33 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.8.0
MIME-Version: 1.0
In-Reply-To: <8ff54c7b-2e64-4503-03f6-1a858d9d5746@redhat.com>
Content-Type: text/plain; charset=utf-8; format=flowed
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 07/04/2016 03:48 PM, Paolo Bonzini wrote:
>
>
> 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.
>

It's clear now.

> 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.

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