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Re: [RFC PATCH] getcpu_cache system call: caching current CPU number (x86)
- From: Florian Weimer <fweimer at redhat dot com>
- To: josh at joshtriplett dot org, Andy Lutomirski <luto at amacapital dot net>
- Cc: Ben Maurer <bmaurer at fb dot com>, Ingo Molnar <mingo at redhat dot com>, libc-alpha <libc-alpha at sourceware dot org>, linux-api <linux-api at vger dot kernel dot org>, Andrew Morton <akpm at linux-foundation dot org>, OndÅej BÃlka <neleai at seznam dot cz>, rostedt <rostedt at goodmis dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>, Lai Jiangshan <laijs at cn dot fujitsu dot com>, Paul Turner <pjt at google dot com>, Andrew Hunter <ahh at google dot com>, Peter Zijlstra <peterz at infradead dot org>
- Date: Tue, 21 Jul 2015 09:55:38 +0200
- Subject: Re: [RFC PATCH] getcpu_cache system call: caching current CPU number (x86)
- Authentication-results: sourceware.org; auth=none
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On 07/20/2015 10:07 PM, josh@joshtriplett.org wrote:
> On Mon, Jul 20, 2015 at 10:41:09AM -0700, Andy Lutomirski wrote:
>> On Mon, Jul 20, 2015 at 8:32 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>> On 07/20/2015 05:31 PM, Andy Lutomirski wrote:
>>>> On Jul 20, 2015 1:35 AM, "Florian Weimer" <fweimer@redhat.com> wrote:
>>>>>
>>>>> On 07/18/2015 01:33 AM, Andy Lutomirski wrote:
>>>>>
>>>>>> I think the API should be "set gsbase to x + y*(cpu number)". On
>>>>>> x86_64, userspace just allocates a big swath of virtual space and
>>>>>> populates it as needed.
>>>>>
>>>>> This will break WINE and similar applications which use %gs today.
>>>>
>>>> Presumably WINE could just opt not to use this facility, just like
>>>> WINE will have to opt out of whatever the enterprise people who want
>>>> WRGSBASE were thinking of doing with it.
>>>
>>> How is this possible if it's process-global attribute and glibc or some
>>> library in the process starts using it?
>>>
>>
>> glibc will have to expose a way to turn it off, I guess. (ELF flag?)
>
> Or a way to turn it on.
How is this supposed to work? Who should turn it on?
It totally breaks encapsulation. We don't need any additional problems
like that.
--
Florian Weimer / Red Hat Product Security