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

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Message-ID: <20201130175706.GA25457@willie-the-truck>
Date:   Mon, 30 Nov 2020 17:57:07 +0000
From:   Will Deacon <will@...nel.org>
To:     Rongwei Wang <rongwei.wang@...ux.alibaba.com>
Cc:     catalin.marinas@....com, 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

On Tue, Dec 01, 2020 at 01:48:30AM +0800, Rongwei Wang wrote:
> MSR ARM driver aims to provide interfacs for user to read or write data to all
> system registers. Its functions is same as MSR driver (x86 platform). It mainly
> depends on kprobe and undef exception to read or write system registers
> dynamicly.

... but why? These are privileged registers for a reason, and giving
userspace access to them is bound to cause serious problems. Why can't we
do whatever it is that userspace is trying to do by poking these things in
the kernel instead? This interface is a bit like using /dev/mem instead of
writing a proper device driver.

Thanks,

Will