linux-kernel - Re: KVM guest sometimes failed to boot because of kernel stack overflow if KPTI is enabled on a hisilicon ARM64 platform.

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Date:   Wed, 27 Jun 2018 14:32:58 +0100
From:   Wei Xu <xuwei5@...ilicon.com>
To:     Will Deacon <will.deacon@....com>
CC:     James Morse <james.morse@....com>, <mark.rutland@....com>,
        <catalin.marinas@....com>, Linuxarm <linuxarm@...wei.com>,
        Zhangyi ac <zhangyi.ac@...wei.com>, <suzuki.poulose@....com>,
        <marc.zyngier@....com>,
        "Xiongfanggou (James)" <james.xiong@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <dave.martin@....com>,
        "Liyuan (Larry, Turing Solution)" <Larry.T@...wei.com>,
        <libeijian@...ilicon.com>, <zhangxiquan@...ilicon.com>,
        <wxf.wang@...ilicon.com>, <dingshuai1@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        "Liguozhu (Kenneth)" <liguozhu@...ilicon.com>
Subject: Re: KVM guest sometimes failed to boot because of kernel stack
 overflow if KPTI is enabled on a hisilicon ARM64 platform.

Hi Will,

On 2018/6/27 14:28, Will Deacon wrote:
> On Wed, Jun 27, 2018 at 02:22:03PM +0100, Wei Xu wrote:
>> On 2018/6/26 18:47, Will Deacon wrote:
>>> If you look at the __idmap_kpti_put_pgtable_ent_ng asm macro, can you try
>>> replacing:
>>>
>>> 	dc      civac, cur_\()\type\()p
>>>
>>> with:
>>>
>>> 	dc      ivac, cur_\()\type\()p
>>>
>>> please? Only do this for the guest kernel, not the host. KVM will upgrade
>>> the clean to a clean+invalidate, so it's interesting to see if this has
>>> an effect on the behaviour.
>>
>> Only changed the guest kernel, the guest still failed to boot and the log
>> is same with the last mail.
>>
>> But if I changed to cvac as below for the guest, it is kind of stable.
>> 	dc      cvac, cur_\()\type\()p
>>
>> I have synced with our SoC guys about this and hope we can find the reason.
>> Do you have any more suggestion?
> 
> Unfortunately, not. It looks like somehow clean+invalidate is behaving
> just as an invalidate, and we're corrupting the page table as a result.
> 
> Hopefully the SoC guys will figure it out.

Thanks anyway!
I will update here if any news.

Best Regards,
Wei

> 
> Will
> 
> .
>