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From: Andy Lutomirski <luto@amacapital.net>
Date: Sun, 3 Apr 2016 06:55:00 -0700
Message-ID: <CALCETrX_x+tV4m3SwgCfXg9y5gia8eMhhTdUnHuXpXhnULkHRw@mail.gmail.com>
Subject: Re: [PATCH v5 4/9] x86/traps: Enable all exception handler callbacks early
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, KVM list <kvm@vger.kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        xen-devel <Xen-devel@lists.xen.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
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On Sun, Apr 3, 2016 at 6:51 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Sun, Apr 3, 2016 at 3:07 AM, Borislav Petkov <bp@alien8.de> wrote:
>>
>> I'm wondering whether making it try to EFAULT correctly is the right
>> thing to do... We're certainly more conservative if we panic and not
>> allow some silently failed attempt at recovery which looks successful,
>> to continue.
>
> No, please don't fail at early boot.
>
> Early boot is just about the *worst* situation to try to debug odd
> failures, exactly since things like printk may not be reliable, and
> things won't get logged etc.
>
> So particularly during early boot we should try as hard as possible
> not to crash - even if it means not being able to log about a problem.
> At least that way you have a hopefully working machine and can *maybe*
> debug things.
>

In this regard, at least, my patch is the right approach.  Calling the
handler, whatever it is, is less likely to panic than refusing to call
it.

--Andy