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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Message-ID: <20180622133133.GA1802@arm.com>
Date:   Fri, 22 Jun 2018 14:31:34 +0100
From:   Will Deacon <will.deacon@....com>
To:     Wei Xu <xuwei5@...ilicon.com>
Cc:     James Morse <james.morse@....com>, catalin.marinas@....com,
        suzuki.poulose@....com, dave.martin@....com, mark.rutland@....com,
        marc.zyngier@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Linuxarm <linuxarm@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>, xiexiuqi@...wei.com,
        huangdaode <huangdaode@...ilicon.com>,
        "Chenxin (Charles)" <charles.chenxin@...wei.com>,
        "Xiongfanggou (James)" <james.xiong@...wei.com>,
        "Liguozhu (Kenneth)" <liguozhu@...ilicon.com>,
        Zhangyi ac <zhangyi.ac@...wei.com>,
        jonathan.cameron@...wei.com,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        John Garry <john.garry@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        Shiju Jose <shiju.jose@...wei.com>,
        "Zhuangyuzeng (Yisen)" <yisen.zhuang@...wei.com>,
        "Wangzhou (B)" <wangzhou1@...ilicon.com>,
        "kongxinwei (A)" <kong.kongxinwei@...ilicon.com>,
        "Liyuan (Larry, Turing Solution)" <Larry.T@...wei.com>,
        libeijian@...ilicon.com, zhangbin011@...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 again, Wei,

On Fri, Jun 22, 2018 at 09:18:27PM +0800, Wei Xu wrote:
> On 2018/6/22 19:16, Will Deacon wrote:
> >On Fri, Jun 22, 2018 at 06:45:15PM +0800, Wei Xu wrote:
> >>On 2018/6/22 17:23, Will Deacon wrote:
> >>>Perhaps just writing back the table entries is enough to cause the issue,
> >>>although I really can't understand why that would be the case. Can you try
> >>>the diff below (without my previous change), please?
> >>Thanks!
> >>But it does not resolve the issue(only apply this patch based on 4.17.0).
> >Thanks, that's a useful data point. It means that it still crashes even if
> >we write back the same table entries, so it's the fact that we're writing
> >them at all which causes the problem, not the value that we write.
> >
> >Whilst looking at the code, we noticed a missing DMB. On the off-chance
> >that it helps, can you try this instead please?
> Thanks!
> Only apply below patch based on 4.17.0, we still got the crash.

Oh well, it was worth a shot (and that's still a fix worth having). Please
can you provide the complete disassembly for kpti_install_ng_mappings()
(I'm referring to the C function in cpufeature.c) along with a corresponding
crash log so that we can correlate the instruction stream with the crash?

Thanks,

Will