Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <76b50214-fcf8-37fe-47c9-cfcaf7517048@huawei.com>
Date:   Fri, 26 May 2023 09:57:40 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.10.1
Subject: Re: [PATCH] x86/mce: set MCE_IN_KERNEL_COPYIN for all MC-Safe Copy
Content-Language: en-US
To:     Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        <linux-edac@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-mm@kvack.org>, <jane.chu@oracle.com>
References: <20230508022233.13890-1-wangkefeng.wang@huawei.com>
 <5570c23a-3b12-6685-cb0b-29fc1d58f541@intel.com>
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
In-Reply-To: <5570c23a-3b12-6685-cb0b-29fc1d58f541@intel.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 2023/5/26 1:18, Dave Hansen wrote:
> On 5/7/23 19:22, Kefeng Wang wrote:
>> Both EX_TYPE_FAULT_MCE_SAFE and EX_TYPE_DEFAULT_MCE_SAFE exception
>> fixup types are used to identify fixups which allow in kernel #MC
>> recovery, that is the Machine Check Safe Copy.
>>
>> For now, the MCE_IN_KERNEL_COPYIN flag is only set for EX_TYPE_COPY
>> and EX_TYPE_UACCESS when copy from user, and corrupted page is
>> isolated in this case, for MC-safe copy, memory_failure() is not
>> always called, some places, like __wp_page_copy_user, copy_subpage,
>> copy_user_gigantic_page and ksm_might_need_to_copy manually call
>> memory_failure_queue() to cope with such unhandled error pages,
>> recently coredump hwposion recovery support[1] is asked to do the
>> same thing, and there are some other already existed MC-safe copy
>> scenarios, eg, nvdimm, dm-writecache, dax, which has similar issue.
> 
> That has to set some kind of record for run-on sentences.  Could you
> please try to rewrite this coherently?
> 
>> The best way to fix them is set MCE_IN_KERNEL_COPYIN to MCE_SAFE
>> exception, then kill_me_never() will be queued to call memory_failure()
>> in do_machine_check() to isolate corrupted page, which avoid calling
>> memory_failure_queue() after every MC-safe copy return.
> 
> Could you try to send a v2 of this with a clear problem statement?
> 

:( will try to make it more clear.

> What is the end user visible effect of the problem and of your solution?

The corrupted page won't be isolated for MC-safe copy scenario, and it 
could be accessed again by use application.