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

[Ingo Molnar <mingo@xxxxxxxxxx>]

* Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:

> On Thu, Oct 1, 2015 at 12:15 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> >
> > * Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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.
> 
> Just a heads up: the extable improvements in tip:ras/core make it
> straightforward to get the best of all worlds: explicit failure
> handling (written in C!), no fast path overhead whatsoever, and no new
> garbage in the exception handlers.

I _knew_ I should have merged them into tip:x86/mm, not tip:ras/core ;-)

I had a quick look at your new MSR series and I'm very happy with that 
direction!

Thanks,

        Ingo

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