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

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On 9/21/2015 9:36 AM, Linus Torvalds wrote:
> 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?

if anything qualifies it'd be switch_to() and friends.

note that I'm not entirely happy about the notion of "safe" MSRs.
They're safe as in "won't fault".
Reading random MSRs isn't a generic safe operation though, but the name sort of gives people
the impression that it is. Even with _safe variants, you still need to KNOW the MSR exists (by means
of CPUID or similar) unfortunately.


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[PATCH v2 0/2] x86/msr: MSR access failure changes Andy Lutomirski <luto@kernel.org> - 2015-09-21 02:10 +0200
  [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@kernel.org> - 2015-09-21 02:10 +0200
    Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-21 02:20 +0200
      Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2015-09-21 03:20 +0200
        Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2015-09-21 10:50 +0200
          Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-21 14:30 +0200
          Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-21 18:40 +0200
            Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Arjan van de Ven <arjan@linux.intel.com> - 2015-09-21 19:10 +0200
              Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-21 19:30 +0200
              Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2015-09-21 19:50 +0200
                Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Paolo Bonzini <pbonzini@redhat.com> - 2015-09-22 10:20 +0200
            Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2015-09-21 20:20 +0200
              Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Borislav Petkov <bp@alien8.de> - 2015-09-21 20:40 +0200
              Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-21 20:50 +0200
            Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2015-09-22 09:20 +0200
            Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Peter Zijlstra <peterz@infradead.org> - 2015-09-30 15:20 +0200
              Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2015-09-30 16:10 +0200
                Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2015-09-30 20:10 +0200
                Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2015-10-01 09:20 +0200
            Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access  fails without !panic_on_oops "H. Peter Anvin" <hpa@zytor.com> - 2015-09-30 20:40 +0200
  [PATCH v2 2/2] x86/msr: Set the return value to zero when native_rdmsr_safe fails Andy Lutomirski <luto@kernel.org> - 2015-09-21 02:10 +0200

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