linux-kernel - Re: [PATCH] x86, traps: install gates using IST after cpu

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Date:	Thu, 26 Feb 2015 07:14:00 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] x86, traps: install gates using IST after cpu_init().

On Wed, Feb 25, 2015 at 10:15 PM, Wang Nan <wangnan0@...wei.com> wrote:
> X86_TRAP_NMI, X86_TRAP_DF and X86_TRAP_MC use their own stack. Those
> stacks are invalid until cpu_init() installs TSS.
>
> This patch moves setting of the 3 gates after cpu_init().
>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---
>
> If I understand correctly, logically speaking the original code is
> incorrect.  However, there is no real bug caused by it for serval years.
> I'm not sure whether this fix is practical or not. Fix them only for
> logical correctness.

Acked-by: Andy Lutomirski <luto@...capital.net>

That being said, I'm pretty sure you're not fixing a bug here.
Delivery of an exception with no handler is every bit as fatal as
delivery of an exception with a non-working IST handler.

--Andy
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