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 S1752558AbeBIDWS (ORCPT <rfc822;w@1wt.eu>);
        Thu, 8 Feb 2018 22:22:18 -0500
Received: from mail-io0-f196.google.com ([209.85.223.196]:46056 "EHLO
        mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1752509AbeBIDWR (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 8 Feb 2018 22:22:17 -0500
X-Google-Smtp-Source: AH8x225cHqqkjEYa3feF1Rtfdekw4oJvJ0ER77QAeTJy0sdVlUiA4mMfgZD5h3yq4Su2SR4eJvnAaw==
Subject: Re: [PATCH] KVM: X86: Fix SMRAM accessing even if VM is shutdown
To: Paolo Bonzini <pbonzini@redhat.com>, Wanpeng Li <kernellwp@gmail.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Dmitry Vyukov <dvyukov@google.com>
References: <1517984706-47244-1-git-send-email-wanpengli@tencent.com>
 <233cfca3-971e-c3c2-f0fe-b50dd69d2546@redhat.com>
 <d21822e2-2982-7182-1d9a-be3e5b7e1553@gmail.com>
 <5664ca7f-f391-0301-3a0d-666b73f17b15@redhat.com>
From: Xiao Guangrong <guangrong.xiao@gmail.com>
Message-ID: <9034fe13-26c4-ee72-5b94-19aa8fc11efc@gmail.com>
Date: Fri, 9 Feb 2018 11:22:44 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.2
MIME-Version: 1.0
In-Reply-To: <5664ca7f-f391-0301-3a0d-666b73f17b15@redhat.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
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 02/08/2018 06:31 PM, Paolo Bonzini wrote:
> On 08/02/2018 09:57, Xiao Guangrong wrote:
>>> Maybe it should return RET_PF_EMULATE, which would cause an emulation
>>> failure and then an exit with KVM_EXIT_INTERNAL_ERROR.
>>
>> So the root cause is that a running vCPU accessing the memory whose memslot
>> is being updated (met the condition KVM_MEMSLOT_INVALID is set on the its
>> memslot).
>>
>> The normal #PF handler breaks KVM_RUN and returns -EFAULT to userspace,
>> we'd better to make ept-misconfig's handler follow this style as well.
> 
> Why return -EFAULT and not attempt emulation (which will fail)?
> 

That is a good question... :)

This case (with KVM_MEMSLOT_INVALID is set) can be easily constructed,
userspace should avoid this case by itself (avoiding vCPU accessing the
memslot which is being updated). If it happens, it's a operation issue
rather than INTERNAL ERROR.

Maybe treat it as MMIO accessing and return to userspace with MMIO_EXIT
is a better solution...