linux-kernel - Re: [PATCH 3/4] x86: save user rsp in pt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 10 Mar 2015 14:26:06 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86: save user rsp in pt_regs->sp on SYSCALL64
 fastpath


* Andy Lutomirski <luto@...capital.net> wrote:

> > Since this patch does add two extra MOVs,
> > I did benchmark these patches. They add exactly one cycle
> > to system call code path on my Sandy Bridge CPU.
> 
> Personally, I'm willing to pay that cycle.  It could be a bigger 
> savings on context switch, and the simplification it enables is 
> pretty good.

But, but ... context switches are a relative slow path, compared to 
system calls. And I say this with the scheduler maintainer hat on as 
well.

So this is not a good bargain IMHO, assuming it's not some _huge_ 
difference in maintainability - but having an extra percpu field
isn't really much of a problem.

I don't claim that we couldn't in some other situation decide that a 
certain type of speedup isn't worth it - but what's the big problem 
here? A bit of arithmetics shouldn't be a problem?

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/