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, 20 Jun 2018 17:28:45 +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
Subject: Re: KVM guest sometimes failed to boot because of kernel stack
 overflow if KPTI is enabled on a hisilicon ARM64 platform.

On Thu, Jun 21, 2018 at 12:25:05AM +0800, Wei Xu wrote:
> Hi James,
> 
> On 2018/6/20 23:54, James Morse wrote:
> >Hi Wei,
> >
> >On 20/06/18 16:52, Wei Xu wrote:
> >>On 2018/6/20 22:42, Will Deacon wrote:
> >>>Hmm, I wonder if this is at all related to RAS, since we've just enabled
> >>>that and if we take a fault whilst rewriting swapper then we're going to
> >>>get stuck. What happens if you set CONFIG_ARM64_RAS_EXTN=n in the guest?
> >>I will try it now.
> >It's not just the Kconfig symbol, could you also revert:
> >
> >f751daa4f9d3 ("arm64: Unconditionally enable IESB on exception entry/return for
> >firmware-first")
> >
> >
> >(reverts and build cleanly on 4.17)
> 
> Thanks to point out this!
> I have disabled CONFIG_ARM64_RAS_EXTN and reverted that commit.
> But I still got the stack overflow issue sometimes.
> Do you have more hint?

[...]

>     [    0.076797] pstate: 604003c5 (nZCv DAIF +PAN -UAO)
>     [    0.081727] pc : el1_sync+0x0/0xb0
>     [    0.085217] lr : kpti_install_ng_mappings+0x120/0x214

Please run:

$ ./scripts/faddr2line vmlinux kpti_install_ng_mappings+0x120/0x214

as the GDB output wasn't helpful (it only showed local variable
declarations?!).

Will