From: Wei Xu <xuwei5@hisilicon.com>
To: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>, <catalin.marinas@arm.com>,
<suzuki.poulose@arm.com>, <dave.martin@arm.com>,
<mark.rutland@arm.com>, <marc.zyngier@arm.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, Linuxarm <linuxarm@huawei.com>,
Hanjun Guo <guohanjun@huawei.com>, <xiexiuqi@huawei.com>,
huangdaode <huangdaode@hisilicon.com>,
"Chenxin (Charles)" <charles.chenxin@huawei.com>,
"Xiongfanggou (James)" <james.xiong@huawei.com>,
"Liguozhu (Kenneth)" <liguozhu@hisilicon.com>,
Zhangyi ac <zhangyi.ac@huawei.com>, <jonathan.cameron@huawei.com>,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
John Garry <john.garry@huawei.com>,
Salil Mehta <salil.mehta@huawei.com>,
Shiju Jose <shiju.jose@huawei.com>,
"Zhuangyuzeng (Yisen)" <yisen.zhuang@huawei.com>,
"Wangzhou (B)" <wangzhou1@hisilicon.com>,
"kongxinwei (A)" <kong.kongxinwei@hisilicon.com>,
"Liyuan (Larry, Turing Solution)" <Larry.T@huawei.com>,
<libeijian@hisilicon.com>, <zhangbin011@hisilicon.com>
Subject: Re: KVM guest sometimes failed to boot because of kernel stack overflow if KPTI is enabled on a hisilicon ARM64 platform.
Date: Fri, 22 Jun 2018 09:33:04 +0100 [thread overview]
Message-ID: <5B2CB440.8040705@hisilicon.com> (raw)
In-Reply-To: <20180621105404.GB22505@arm.com>
Hi Will,
On 2018/6/21 11:54, Will Deacon wrote:
> Hi Wei,
>
> On Thu, Jun 21, 2018 at 11:14:28AM +0100, Wei Xu wrote:
>> On 2018/6/21 10:18, Will Deacon wrote:
>>> On Thu, Jun 21, 2018 at 09:38:53AM +0100, James Morse wrote:
>>>> On 20/06/18 17:25, Wei Xu wrote:
>>>>> [ 0.042421] Insufficient stack space to handle exception!
>>>>> [ 0.042423] ESR: 0x96000046 -- DABT (current EL)
>>>>> [ 0.043730] FAR: 0xffff0000093a80e0
>>>>> [ 0.044714] Task stack: [0xffff0000093a8000..0xffff0000093ac000]
>>>>
>>>> This was a level 2 translation fault on a write, to an address that is within
>>>> the stack....
>>>>
>>>>
>>>>> [ 0.051113] IRQ stack: [0xffff000008000000..0xffff000008004000]
>>>>> [ 0.057610] Overflow stack: [0xffff80003efce2f0..0xffff80003efcf2f0]
>>>>> [ 0.064003] CPU: 0 PID: 12 Comm: migration/0 Not tainted
>>>>> 4.17.0-45865-g2b31fe7-dirty #10
>>>>> [ 0.072201] Hardware name: linux,dummy-virt (DT)
>>>>
>>>>> [ 0.076797] pstate: 604003c5 (nZCv DAIF +PAN -UAO)
>>>>> [ 0.081727] pc : el1_sync+0x0/0xb0
>>>>
>>>> ... from the vectors.
>>>>
>>>>
>>>>> [ 0.085217] lr : kpti_install_ng_mappings+0x120/0x214
>>>>
>>>> What I think is happening is: we come out of the kpti idmap with the stack
>>>> unmapped. Shortly after we access the stack, which faults. el1_sync faults as
>>>> well when it tries to push the registers to the stack, and we keep going until
>>>> we overflow the stack.
>>>>
>>>> I can't reproduce this with kvmtool or qemu in the model.
>>>
>>> Hmm, one thing that occurs to me is that the kpti_install_ng_mappings()
>>> code leaves the nG bit set in table entries, which is actually IGNORED in
>>> the architecture.
>>>
>>> Wei -- does the diff below help at all? Make sure you disable CONFIG_KASAN,
>>> otherwise your kernel will take an age to boot.
>>
>> Yes, amazing! This patch resolved the issue.
>
> Great...
>
>> I have tested 50 times and can not reproduce the issue any more.
>> Could you please tell more why this patch works?
>
> You might need to ask your CPU design team ;)
>
> Without this patch, the code in idmap_kpti_install_ng_mappings() sets
> bit 11 in table descriptors so that we can keep track of which parts of
> the page table we've visited. With this patch, we don't bother tracking
> and potentially rewalk parts of the page table (which takes a very long
> time if KASAN is enabled).
Got it. Thanks!
>
> The architecture documents I've looked at are clear that bit 11 is IGNORED
> by the CPU, which:
>
> "Indicates that the architecture guarantees that the bit or field is not
> interpreted or modified by hardware."
>
> Please can you double-check that your CPU is indeed ignoring bit 11 in
> non-leaf (table) descriptors?
Do the non-leaf(table) descriptors mean the table descriptors
of the section D4.3.1 "VMSAv8-64 translation table level 0, level 1, and level 2 descriptor formats"
in the ARM Architecture Reference Manual ARMv8 for ARMv8-A(DDI0487C_a_armv8_arm.pdf)?
If yes, our hardware does ignore it(not interpret or modify).
Is there any other possible reason cause this?
Thanks!
Best Regards,
Wei
>
> Thanks,
>
> Will
>
> .
>
next prev parent reply other threads:[~2018-06-22 8:33 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 14:18 KVM guest sometimes failed to boot because of kernel stack overflow if KPTI is enabled on a hisilicon ARM64 platform Wei Xu
2018-06-20 14:42 ` Will Deacon
2018-06-20 15:52 ` Wei Xu
2018-06-20 15:54 ` James Morse
2018-06-20 16:25 ` Wei Xu
2018-06-20 16:28 ` Will Deacon
2018-06-20 16:33 ` Wei Xu
2018-06-21 8:38 ` James Morse
2018-06-21 9:00 ` Marc Zyngier
2018-06-21 9:18 ` Will Deacon
2018-06-21 10:14 ` Wei Xu
2018-06-21 10:54 ` Will Deacon
2018-06-22 8:33 ` Wei Xu [this message]
2018-06-22 9:23 ` Will Deacon
2018-06-22 10:45 ` Wei Xu
2018-06-22 11:16 ` Will Deacon
2018-06-22 13:18 ` Wei Xu
2018-06-22 13:31 ` Will Deacon
2018-06-22 13:46 ` Wei Xu
2018-06-22 14:43 ` Will Deacon
2018-06-22 15:26 ` Wei Xu
2018-06-22 14:28 ` Mark Rutland
2018-06-22 15:28 ` Wei Xu
2018-06-22 15:41 ` Will Deacon
2018-06-22 16:02 ` Wei Xu
2018-06-21 9:20 ` Wei Xu
2018-06-26 17:16 ` Wei Xu
2018-06-26 17:47 ` Will Deacon
2018-06-27 8:39 ` James Morse
2018-06-27 13:26 ` Wei Xu
2018-06-28 8:45 ` James Morse
2018-06-28 10:20 ` Wei Xu
2018-06-27 13:22 ` Wei Xu
2018-06-27 13:28 ` Will Deacon
2018-06-27 13:32 ` Wei Xu
2018-06-28 14:50 ` Wei Xu
2018-06-28 15:34 ` Mark Rutland
[not found] ` <etPan.5b3507f7.914aa16.1d6b@localhost>
2018-06-28 16:24 ` 答复: " Mark Rutland
2018-06-29 9:59 ` Mark Rutland
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