linux-kernel - Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on

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Message-ID: <CALCETrUBcDxvtjKC-m97GPwCOHvcoDdGjnMJLukSue8ha55mng@mail.gmail.com>
Date:	Mon, 21 Sep 2015 11:16:30 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KVM list <kvm@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access
 fails without !panic_on_oops

On Mon, Sep 21, 2015 at 9:36 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Mon, Sep 21, 2015 at 1:46 AM, Ingo Molnar <mingo@...nel.org> wrote:
>>
>> Linus, what's your preference?
>
> So quite frankly, is there any reason we don't just implement
> native_read_msr() as just
>
>    unsigned long long native_read_msr(unsigned int msr)
>    {
>       int err;
>       unsigned long long val;
>
>       val = native_read_msr_safe(msr, &err);
>       WARN_ON_ONCE(err);
>       return val;
>    }
>
> Note: no inline, no nothing. Just put it in arch/x86/lib/msr.c, and be
> done with it. I don't see the downside.

In the interest of sanity, I want to drop the "native_", too, since
there appear to be few or no good use cases for native_read_msr as
such.  I'm tempted to add new functions read_msr and write_msr that
forward to rdmsrl_safe and wrmsrl_safe.

It looks like the msr helpers are every bit as bad as the TSC helpers
used to be :(

--Andy
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