Re: [x86/asm/entry] BUG: unable to handle kernel paging request

From: Denys Vlasenko
Date: Mon Mar 09 2015 - 08:05:22 EST

On Mon, Mar 9, 2015 at 12:46 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> * Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> >> */
>> >> unsigned long stack[64];
>> >>
>> >> Last I checked, 0x100 != 64. Also, wow, this is kind of disgusting. :)
>> >
>> >
>> > Seems to be unused: I commented it out on "defconfig" build
>> > and got no build errors.
>> It's used. On 32-bit, NMIs don't use task gates (I don't know why),
> So task gates were a sexy hardware acceleration feature, eons ago, and
> we used to rely on them a lot,

IIRC task gates weren't used in Linux at first, and now they are
only used for double fault handler - because in many cases
double fault is caused by stack problems, and task gate provides
a way to have alternative stack even for exceptions happening
in CPL0.
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