From: Brian Gerst <brgerst@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Tony Luck <tony.luck@intel.com>, Ingo Molnar <mingo@kernel.org>,
Borislav Petkov <bp@alien8.de>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Dan Williams <dan.j.williams@intel.com>, Robert <elliott@hpe.com>,
"linux-kernel@vger.kernel.org" <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>
Subject: Re: [PATCH v8 1/3] x86: Expand exception table to allow new handling options
Date: Fri, 8 Jan 2016 23:31:16 -0500 [thread overview]
Message-ID: <CAMzpN2jAvhM74ZGNecnqU3ozLUXb185Cb2iZN6LB0bToFo4Xhw@mail.gmail.com> (raw)
In-Reply-To: <CAMzpN2j=ZRrL=rXLOTOoUeodtu_AqkQPm1-K0uQmVwLAC6MQGA@mail.gmail.com>
On Fri, Jan 8, 2016 at 10:39 PM, Brian Gerst <brgerst@gmail.com> wrote:
> On Fri, Jan 8, 2016 at 8:52 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> On Fri, Jan 8, 2016 at 12:49 PM, Tony Luck <tony.luck@intel.com> wrote:
>>> Huge amounts of help from Andy Lutomirski and Borislav Petkov to
>>> produce this. Andy provided the inspiration to add classes to the
>>> exception table with a clever bit-squeezing trick, Boris pointed
>>> out how much cleaner it would all be if we just had a new field.
>>>
>>> Linus Torvalds blessed the expansion with:
>>> I'd rather not be clever in order to save just a tiny amount of space
>>> in the exception table, which isn't really criticial for anybody.
>>>
>>> The third field is a simple integer indexing into an array of handler
>>> functions (I thought it couldn't be a relative pointer like the other
>>> fields because a module may have its ex_table loaded more than 2GB away
>>> from the handler function - but that may not be actually true. But the
>>> integer is pretty flexible, we are only really using low two bits now).
>>>
>>> We start out with three handlers:
>>>
>>> 0: Legacy - just jumps the to fixup IP
>>> 1: Fault - provide the trap number in %ax to the fixup code
>>> 2: Cleaned up legacy for the uaccess error hack
>>
>> I think I preferred the relative function pointer approach.
>>
>> Also, I think it would be nicer if the machine check code would invoke
>> the handler regardless of which handler (or class) is selected. Then
>> the handlers that don't want to handle #MC can just reject them.
>>
>> Also, can you make the handlers return bool instead of int?
>
> I'm hashing up an idea that could eliminate alot of text in the .fixup
> section, but it needs the integer handler method to work. We have
> alot of fixup code that does "mov $-EFAULT, reg; jmp xxxx". If we
> encode the register in the third word, the handler can be generic and
> no fixup code for each user access would be needed. That would
> recover alot of the memory used by expanding the exception table.
On second thought, this could still be implemented with a relative
function pointer. We'd just need a separate function for each
register.
--
Brian Gerst
next prev parent reply other threads:[~2016-01-09 4:31 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-09 0:04 [PATCH v8 0/3] Machine check recovery when kernel accesses poison Tony Luck
2015-12-31 19:40 ` [PATCH v8 2/3] x86, mce: Check for faults tagged in EXTABLE_CLASS_FAULT exception table entries Tony Luck
2016-01-08 20:49 ` [PATCH v8 1/3] x86: Expand exception table to allow new handling options Tony Luck
2016-01-09 1:52 ` Andy Lutomirski
2016-01-09 3:39 ` Brian Gerst
2016-01-09 4:31 ` Brian Gerst [this message]
2016-01-09 6:36 ` Andy Lutomirski
2016-01-11 23:09 ` Brian Gerst
2016-01-11 23:22 ` Andy Lutomirski
2016-01-11 23:48 ` Luck, Tony
2016-01-09 17:45 ` Tony Luck
2016-01-09 18:00 ` Andy Lutomirski
2016-01-09 19:51 ` Tony Luck
2016-01-09 22:32 ` Andy Lutomirski
2016-01-10 1:15 ` Tony Luck
2016-01-11 0:25 ` Luck, Tony
2016-01-08 21:18 ` [PATCH v8 3/3] x86, mce: Add __mcsafe_copy() Tony Luck
2016-01-09 1:49 ` Andy Lutomirski
2016-01-09 17:48 ` Tony Luck
2016-01-09 17:57 ` Andy Lutomirski
2016-01-09 19:39 ` Tony Luck
2016-01-09 22:15 ` Dan Williams
2016-01-09 22:33 ` Andy Lutomirski
2016-01-10 0:23 ` Dan Williams
2016-01-10 1:40 ` Tony Luck
2016-01-10 11:26 ` Borislav Petkov
2016-01-11 10:44 ` Ingo Molnar
2016-01-13 23:22 ` Tony Luck
2016-01-14 4:39 ` Borislav Petkov
2016-01-30 0:35 ` Tony Luck
2016-01-30 10:28 ` Borislav Petkov
2016-02-01 23:10 ` Tony Luck
2016-02-01 23:16 ` Dan Williams
2016-01-12 0:26 ` Luck, Tony
2016-01-12 0:30 ` Andy Lutomirski
2016-01-12 0:37 ` Andy Lutomirski
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