linux-kernel - Re: [RFC 1/3] x86: Add this_cpu_sp0() to read sp0 for the current cpu

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Message-ID: <CALCETrXi_RFCOwLvsgP8xsJ7-bFayK5OdJ+ROrhhO9S7w6sW_A@mail.gmail.com>
Date:	Wed, 4 Mar 2015 10:51:44 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC 1/3] x86: Add this_cpu_sp0() to read sp0 for the current cpu

On Wed, Mar 4, 2015 at 12:02 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...capital.net> wrote:
>
>> We currently store references to the top of the kernel stack in
>> multiple places: kernel_stack (with an offset) and
>> init_tss.x86_tss.sp0 (no offset).  The latter is defined by hardware
>> and is a clean canonical way to find the top of the stack.  Add an
>
> Btw., 'per_cpu(init_tss)' is a somewhat misleading name these days, as
> there's nothing 'init' about it anymore - we load it during CPU init
> and then manually maintain its contents. A better name would be
> 'current_tss' - referring to both the current CPU and the current
> task?

Hmm.  That seems a little odd to me, since we never change the TSS
pointer.  It's certainly better than init_tss, though.  I'll add a
followup to rename it.

>
>> This needs minor paravirt tweaks to ensure that On native, sp0
>
> nit: s/On/on/
>
>> defines the top of the kernel stack.  On Xen and lguest, the
>> hypervisor tracks it, but we want to start reading sp0 in the
>> kernel.  Fixing this is simple: just update our local copy of sp0 as
>> well as the hypervisor's copy on task switches.

Thanks,
Andy
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