linux-kernel - Re: [PATCH v5 4/9] x86/traps: Enable all exception handler callbacks early

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Message-ID: <CALCETrX_x+tV4m3SwgCfXg9y5gia8eMhhTdUnHuXpXhnULkHRw@mail.gmail.com>
Date:	Sun, 3 Apr 2016 06:55:00 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	KVM list <kvm@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 4/9] x86/traps: Enable all exception handler callbacks early

On Sun, Apr 3, 2016 at 6:51 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Sun, Apr 3, 2016 at 3:07 AM, Borislav Petkov <bp@...en8.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