linux-kernel - Re: [PATCH v5 2/4] x86/ldt: Make modify

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Message-ID: <55CD06A4.2090100@zytor.com>
Date:	Thu, 13 Aug 2015 14:05:40 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	"security@...nel.org" <security@...nel.org>,
	X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	xen-devel <xen-devel@...ts.xen.org>, stable@...r.kernel.org
Subject: Re: [PATCH v5 2/4] x86/ldt: Make modify_ldt synchronous

On 07/27/2015 10:29 PM, Andy Lutomirski wrote:
> modify_ldt has questionable locking and does not synchronize
> threads.  Improve it: redesign the locking and synchronize all
> threads' LDTs using an IPI on all modifications.
> 
> This will dramatically slow down modify_ldt in multithreaded
> programs, but there shouldn't be any multithreaded programs that
> care about modify_ldt's performance in the first place.
> 

<nitpick>

... except 32-bit programs compiled with one specific version of glibc.
 Do we care?  I don't think so.

</nitpick>


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