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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Date:	Mon, 21 Sep 2015 10:27:49 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	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>
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 9:49 AM, Arjan van de Ven <arjan@...ux.intel.com> wrote:
>>
>> How many msr reads are <i>so</i> critical that the function call
>> overhead would matter?
>
> if anything qualifies it'd be switch_to() and friends.

Is there anything else than the FS/GS_BASE thing (possibly hidden
behind inlines etc that I didn't get from a quick grep)? And why is
that sometimes using the "safe" version (in do_arch_prctl()), and
sometimes not (switch_to())?

I'm not convinced that mess is a good argument for the status quo ;)

> note that I'm not entirely happy about the notion of "safe" MSRs.
> They're safe as in "won't fault".

I wouldn't object to renaming them.

                Linus
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