From: Andy Lutomirski <luto@amacapital.net>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
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>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.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 10:43:44 -0700 [thread overview]
Message-ID: <CALCETrUSEm_QLxGaBdmy3tQn=WnagvzTaYpy+i14sGUeaOUvTQ__17221.9548644081$1442857542$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <56003506.1050100@linux.intel.com>
On Mon, Sep 21, 2015 at 9:49 AM, Arjan van de Ven <arjan@linux.intel.com> wrote:
> 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.
And maybe the KVM user return notifier. Unfortunately, switch_to
might gain another two MSR accesses at some point if we decide to fix
the bugs in there. Sigh.
>
> 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.
>
I tend to agree.
Anyway, the fully out-of-line approach isn't obviously a bad idea, and
it simplifies the whole mess (we can drop most of the paravirt
patches, too). I'll give it a try and see what happens.
--Andy
next prev parent reply other threads:[~2015-09-21 17:43 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1442793572.git.luto@kernel.org>
2015-09-21 0:02 ` [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski
2015-09-21 0:02 ` [PATCH v2 2/2] x86/msr: Set the return value to zero when native_rdmsr_safe fails Andy Lutomirski
[not found] ` <130a3b7ef4788baae3a6fe71293ab17442bc9a0a.1442793572.git.luto@kernel.org>
2015-09-21 0:15 ` [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Linus Torvalds
[not found] ` <CA+55aFy4Chd-PJvxGne=TztPsvFqUG07Ht8mtc4+0oGNZNDOyw@mail.gmail.com>
2015-09-21 1:13 ` Andy Lutomirski
[not found] ` <CALCETrXqsKcqzfqMO2ctOJJ4X8Kb6vvoUpVDir9F2-a3XwK23w@mail.gmail.com>
2015-09-21 8:46 ` Ingo Molnar
[not found] ` <20150921084642.GA30984@gmail.com>
2015-09-21 12:27 ` Paolo Bonzini
2015-09-21 16:36 ` Linus Torvalds
[not found] ` <CA+55aFzKCi6pf0RP8HjDQYDsms6reB5AihuCAHEkVJtoOHk_Yw@mail.gmail.com>
2015-09-21 16:49 ` Arjan van de Ven
[not found] ` <56003506.1050100@linux.intel.com>
2015-09-21 17:27 ` Linus Torvalds
2015-09-21 17:43 ` Andy Lutomirski [this message]
[not found] ` <CALCETrUSEm_QLxGaBdmy3tQn=WnagvzTaYpy+i14sGUeaOUvTQ@mail.gmail.com>
2015-09-22 8:12 ` Paolo Bonzini
2015-09-21 18:16 ` Andy Lutomirski
[not found] ` <CALCETrUBcDxvtjKC-m97GPwCOHvcoDdGjnMJLukSue8ha55mng@mail.gmail.com>
2015-09-21 18:36 ` Borislav Petkov
2015-09-21 18:47 ` Linus Torvalds
2015-09-22 7:14 ` Ingo Molnar
2015-09-30 13:10 ` Peter Zijlstra
[not found] ` <20150930131002.GK2881@worktop.programming.kicks-ass.net>
2015-09-30 14:01 ` Ingo Molnar
[not found] ` <20150930140122.GB3285@gmail.com>
2015-09-30 18:04 ` Andy Lutomirski
[not found] ` <CALCETrVMV2_3ywQ_t+0rsqzxMm6D9PvDEmOdrie67rRzfj-W_Q@mail.gmail.com>
2015-10-01 7:15 ` Ingo Molnar
[not found] ` <20151001071505.GA21542@gmail.com>
2016-03-11 16:48 ` Andy Lutomirski
[not found] ` <CALCETrUFakwGL9zpj9TwKX9KbG9czq8fpEViU3nWaCvnpGurew@mail.gmail.com>
2016-03-12 16:02 ` Ingo Molnar
2015-09-30 18:32 ` H. Peter Anvin
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