linux-kernel - Re: [RFC PATCH 0/7] x86/entry: Create a home for the x86 entry code in arch/x86/entry/

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Message-ID: <556F450E.1020902@zytor.com>
Date:	Wed, 03 Jun 2015 11:18:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 0/7] x86/entry: Create a home for the x86 entry code
 in arch/x86/entry/

On 06/03/2015 11:04 AM, H. Peter Anvin wrote:
> On 06/03/2015 10:22 AM, Andy Lutomirski wrote:
>>
>> I'm convinced.  If "entry" means entry into code provided by the
>> kernel as opposed to entry via hardware-provided entry mechanism, then
>> the vdso is indeed a pile of entries into the kernel.
>>
> 
> No, it isn't.  It is user space code provided by the kernel.  It is a
> very different beast, and this is highly and unnecessarily confusing.  I
> am thrilled we finally have managed to get the vdso code separated out,
> this just muddles the situation.
> 

So let me clarify this: vdso code is really a kind of system calls, that
just happen to be executed in user space, thus *bypassing* kernel entry.
 We don't want to put all the system call code (or even the x86-specific
ones) in entry/ as that would completely eliminate the point and we have
once again re-invented the kernel/ catch-all.

	-hpa

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