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

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Message-ID: <20150304080210.GA12265@gmail.com>
Date:	Wed, 4 Mar 2015 09:02:10 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	x86@...nel.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


* 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?

> 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,

	Ingo
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