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Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables

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On Fri, Jan 15, 2016 at 5:27 AM, Jean Delvare <jdelvare@suse.de> wrote:
> Hi Andy,
>
> Sorry for the late reply.
>
> On Wed, 13 Jan 2016 14:28:18 -0800, Andy Lutomirski wrote:
>> [cc: Jean Delvare]
>>
>> On Tue, Jan 12, 2016 at 6:25 AM, Pali Rohár <pali.rohar@gmail.com> wrote:
>> > On Monday 11 January 2016 13:58:20 Andy Lutomirski wrote:
>> >> On Sun, Jan 3, 2016 at 6:52 AM, Andy Lutomirski <luto@kernel.org> wrote:
>> >> > The dmi_walk function maps the DMI table, walks it, and unmaps it.
>> >> > This means that the dell_bios_hotkey_table that find_hk_type stores
>> >> > points to unmapped memory by the time it gets read.
>> >> >
>> >> > I've been able to trigger crashes caused by the stale pointer a
>> >> > couple of times, but never on a stock kernel.
>> >> >
>> >> > Fix it by generating the keymap in the dmi_walk callback instead of
>> >> > storing a pointer.
>> >>
>> >> Quick ping: has anyone had a chance to look at this?
>> >
>> > Hi Andy, I looked at this patch, but I think some people from -mm or DMI
>> > code should look at it as it is memory problem... We also has one in
>> > dell-laptop.ko (wrong API usage) and so -mm people could know it better.
>>
>> Let's ask:
>>
>> Jean, am I right that drivers must not store pointers to DMI tables
>> that they find through dmi_walk?
>
> Yes, you are right.
>
>> Is there any alternative interface
>> that could be used to get a longer-lived pointer to DMI tables, or
>> should drivers just parse them and copy out any info needed from the
>> dmi_walk callback?
>
> There is no alternative for OEM type records. Drivers are indeed
> expected to copy the information they need to their own buffers.

FWIW, especially if we consider mapping it persistently, maybe we
should use ioremap_prot and map it both cached and ro.

Actually, switching to a cached mapping regardless of persistence
could noticeably help boot times.  UC accesses are very, very slow.

--Andy

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[PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@kernel.org> - 2016-01-03 16:00 +0100
  Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-11 23:00 +0100
    Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Pali Rohár <pali.rohar@gmail.com> - 2016-01-12 15:30 +0100
      Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-13 23:30 +0100
        Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Michał Kępień <kernel@kempniu.pl> - 2016-01-14 11:00 +0100
          Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-15 14:30 +0100
        Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-01-14 15:10 +0100
          Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-14 21:20 +0100
        Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-15 14:30 +0100
          Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-15 17:30 +0100
            Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-15 19:00 +0100
              Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-15 21:10 +0100
                Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-19 10:20 +0100
  Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Michał Kępień <kernel@kempniu.pl> - 2016-01-14 11:30 +0100
  Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-18 16:50 +0100
    Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-18 19:20 +0100
    Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-18 19:20 +0100
      Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-19 10:20 +0100

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