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

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: KVM list <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	xen-devel <Xen-devel@lists.xen.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@amacapital.net>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
Date: Mon, 21 Sep 2015 09:36:15 -0700	[thread overview]
Message-ID: <CA+55aFzKCi6pf0RP8HjDQYDsms6reB5AihuCAHEkVJtoOHk_Yw__36224.8469297358$1442853469$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <20150921084642.GA30984@gmail.com>

On Mon, Sep 21, 2015 at 1:46 AM, Ingo Molnar <mingo@kernel.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.

How many msr reads are <i>so</i> critical that the function call
overhead would matter? Get rid of the inline version of the _safe()
thing too, and put that thing there too.

                  Linus