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: <20151001071505.GA21542@gmail.com>
Date:	Thu, 1 Oct 2015 09:15:06 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.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>
Subject: Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access
 fails without !panic_on_oops


* Andy Lutomirski <luto@...capital.net> wrote:

> > These could still be open coded in an inlined fashion, like the scheduler usage.
> 
> We could have a raw_rdmsr for those.
> 
> OTOH, I'm still not 100% convinced that this warn-but-don't-die behavior is 
> worth the effort.  This isn't a frequent source of bugs to my knowledge, and we 
> don't try to recover from incorrect cr writes, out-of-bounds MMIO, etc, so do we 
> really gain much by rigging a recovery mechanism for rdmsr and wrmsr failures 
> for code that doesn't use the _safe variants?

It's just the general principle really: don't crash the kernel on bootup. There's 
few things more user hostile than that.

Also, this would maintain the status quo: since we now (accidentally) don't crash 
the kernel on distro kernels (but silently and unsafely ignore the faulting 
instruction), we should not regress that behavior (by adding the chance to crash 
again), but improve upon it.

Thanks,

	Ingo
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