linux-kernel - Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

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Message-ID: <553AB961.3060901@zytor.com>
Date:	Fri, 24 Apr 2015 14:45:05 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <vda.linux@...glemail.com>
CC:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	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>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute
 issue

On 04/24/2015 01:50 PM, Andy Lutomirski wrote:
>>
>> Exactly my feeling. What are you trying to save? About four CPU
>> cycles of checking %ss != __KERNEL_DS on each switch_to?
>> That's not worth bothering about. Your last patch seems to be perfect.
> 
> We'll have to do the write to ss almost every time an AMD CPU sleeps
> in a syscall.  Maybe that's still not a big deal.
> 

Once you're sleeping anyway, I don't think so.

	-hpa


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