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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 4 Jan 2016 15:25:58 -0800
Message-ID: <CALCETrUcuZSp_D-bsZi3i7m2-DKHBOe4KpmJnbR+1bVvbyp5Mw@mail.gmail.com>
Subject: Re: [PATCH v6 1/4] x86: Clean up extable entry format (and free up a bit)
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Sender: owner-linux-mm@kvack.org
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To: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@gmail.com>, Ingo Molnar <mingo@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Dan Williams <dan.j.williams@intel.com>, Robert <elliott@hpe.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, linux-nvdimm <linux-nvdimm@ml01.01.org>, X86-ML <x86@kernel.org>

On Mon, Jan 4, 2016 at 3:02 PM, Borislav Petkov <bp@alien8.de> wrote:
> On Mon, Jan 04, 2016 at 02:29:09PM -0800, Andy Lutomirski wrote:
>> Josh will argue with you if he sees that :)
>
> Except Josh doesn't need allyesconfigs. tinyconfig's __ex_table is 2K.

If we do the make-it-bigger approach, we get a really nice
simplification.  Screw the whole 'class' idea -- just store an offset
to a handler.

bool extable_handler_default(struct pt_regs *regs, unsigned int fault,
unsigned long error_code, unsigned long info)
{
    if (fault == X86_TRAP_MC)
        return false;

    ...
}

bool extable_handler_mc_copy(struct pt_regs *regs, unsigned int fault,
unsigned long error_code, unsigned long info);
bool extable_handler_getput_ex(struct pt_regs *regs, unsigned int
fault, unsigned long error_code, unsigned long info);

and then shove ".long extable_handler_whatever - ." into the extable entry.

Major bonus points to whoever can figure out how to make
extable_handler_iret work -- the current implementation of that is a
real turd.  (Hint: it's not clear to me that it's even possible
without preserving at least part of the asm special case.)

--Andy

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