linux-kernel - Re: [PATCH v2] arm64: invalidate TLB just before turning MMU on

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Message-ID: <bea04814-25d2-7bb2-0f74-0530fcd54210@lca.pw>
Date:   Fri, 14 Dec 2018 20:53:48 -0500
From:   Qian Cai <cai@....pw>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        James Morse <james.morse@....com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] arm64: invalidate TLB just before turning MMU on

On 12/14/18 2:23 AM, Ard Biesheuvel wrote:
> On Fri, 14 Dec 2018 at 05:08, Qian Cai <cai@....pw> wrote:
>> Also tried to move the local TLB flush part around a bit inside
>> __cpu_setup(), although it did complete kdump some times, it did trigger
>> "Synchronous Exception" in EFI after a cold-reboot fairly often that
>> seems no way to recover remotely without reinstalling the OS.
> 
> This doesn't make any sense to me. If the system gets into a weird
> state out of cold reboot, how could this code be the culprit? Please
> check your firmware, and try to reproduce the issue on a system that
> doesn't have such defects.
> 

I'll continue investigating those "Synchronous Exception" although it is kind of
hard due to I don't have any source code of the firmware to confirm it is buggy
or not.

I did manage to reproduce this kdump issue on around 5 of those server running a
fairly recent version of the firmware (07/01/2018). I don't have access to other
large CPU machines.