linux-kernel - Re: [PATCH 0/3] arm64:msr: Add MSR driver

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Date:   Thu, 3 Dec 2020 10:09:36 +0800
From:   Rongwei Wang <rongwei.wang@...ux.alibaba.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     catalin.marinas@....com, Will Deacon <will@...nel.org>,
        bjorn.andersson@...aro.org, shawnguo@...nel.org, vkoul@...nel.org,
        geert+renesas@...der.be, Anson.Huang@....com, michael@...le.cc,
        krzk@...nel.org, olof@...om.net, vincenzo.frascino@....com,
        ardb@...nel.org, masahiroy@...nel.org, gshan@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver



> 2020年12月1日 下午11:25，Borislav Petkov <bp@...en8.de> 写道：
> 
> On Tue, Dec 01, 2020 at 11:17:39PM +0800, Rongwei Wang wrote:
>> In ARM, the system registers can only be accessed through msr and mrs,
>> so the problem created by MSR driver (depend on rdmsr and wrmsr) in
>> x86 is not necessarily present in ARM, which is very different from
>> x86.
> 
> No, the point I'm making is that it doesn't matter what the architecture
> does or does not, register *writes* from userspace are a bad bad idea
> for the reasons I described.
Sorry, I was away for two days and didn't reply in time.
In fact, we find MSR in the x86 architecture to be a particularly useful interface. It helped us a lot when we were doing some kernel debugging. So we consider implementing a similar feature in ARM.
So as a debugging tool, could it exist, e.g. if I change CONFIG_ARM64_MSR to CONFIG_ARM64_MSR_DEBUG or others. Do you think this adjustment is possible?
> 
> -- 
> Regards/Gruss,
>    Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

Regards,
Rongwei Wang.