linux-kernel - Re: [PATCH v6 1/4] x86: Clean up extable entry format (and free up a bit)

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Message-ID: <CALCETrUcuZSp_D-bsZi3i7m2-DKHBOe4KpmJnbR+1bVvbyp5Mw@mail.gmail.com>
Date:	Mon, 4 Jan 2016 15:25:58 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Tony Luck <tony.luck@...il.com>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Robert <elliott@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86-ML <x86@...nel.org>
Subject: Re: [PATCH v6 1/4] x86: Clean up extable entry format (and free up a bit)

On Mon, Jan 4, 2016 at 3:02 PM, Borislav Petkov <bp@...en8.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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