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: <20180629095952.eiyfz6a3vzw6te6u@lakrids.cambridge.arm.com>
Date:   Fri, 29 Jun 2018 10:59:52 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Zhangxiquan <zhangxiquan@...ilicon.com>
Cc:     "Wangxuefeng (E)" <wxf.wang@...ilicon.com>,
        "xuwei (O)" <xuwei5@...wei.com>,
        "will.deacon" <will.deacon@....com>,
        "james.morse" <james.morse@....com>,
        "catalin.marinas" <catalin.marinas@....com>,
        Linuxarm <linuxarm@...wei.com>,
        Zhangyi ac <zhangyi.ac@...wei.com>,
        "suzuki.poulose" <suzuki.poulose@....com>,
        "marc.zyngier" <marc.zyngier@....com>,
        "Xiongfanggou (James)" <james.xiong@...wei.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "dave.martin" <dave.martin@....com>,
        "Liyuan (Larry, Turing Solution)" <Larry.T@...wei.com>,
        Libeijian <libeijian@...ilicon.com>,
        dingshuai <dingshuai1@...wei.com>,
        "Guohanjun (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.

On Thu, Jun 28, 2018 at 07:24:30PM +0000, Zhangxiquan wrote:
> Do you think this order guarantee (between DC and ldst)is applicable for
> cacheable only , or it is also applicable for device ？

This also applies for device memory.

As I quoted previously, from ARM DDI 0487C.a page D3-2069:

  All data cache instructions, other than DC ZVA , that specify an
  address:

  * Can execute in any order relative to loads or stores that access any
    address with the Device memory attribute, or with Normal memory with
    Inner Non-cacheable attribute unless a DMB or DSB is executed
    between the instructions.

i.e. a DMB is sufficient to provide order between DC and loads/stores
which access device memory.

Thanks,
Mark.