From: Andy Lutomirski <luto@amacapital.net>
To: Andi Kleen <andi@firstfloor.org>
Cc: X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Updated version of RD/WR FS/GS BASE patchkit
Date: Mon, 21 Mar 2016 15:47:28 -0700 [thread overview]
Message-ID: <CALCETrXbZuVacSGBUvbcQQqUaqCtmOOXJv_pc=wA4mtnGy-nPQ@mail.gmail.com> (raw)
In-Reply-To: <20160321224152.GH5083@two.firstfloor.org>
On Mon, Mar 21, 2016 at 3:41 PM, Andi Kleen <andi@firstfloor.org> wrote:
>> Imagine that some brilliant lightweight threading library does:
>>
>> - set GS to nonzero (by whatever means -- arch_prctl(ARCH_SET_GS,
>> whatever) on a pre-IVB host followed by migration, some modify_ldt
>> garbage, simple bloody-mindedness, whatever);
>
> Migration is only possible when the CPUID flags match.
>
>> - WRGSBASE
>> - Use GS for a bit
>>
>> This will work most of the time until it gets unlucky with preemption.
>
> As soon as a kernel thread or something else schedules the value
> will be lost.
>
>> And yes, runtime library authors really do mess up in amazing ways.
>>
>> It's an issue. It needs conscious design.
>
> Ok. So your only objection is the order of the context switch
> updates?
No. My objection is that there needs to be an explicit statement what
the semantics are. If the agreed-upon semantics are "undefined
behavior if GS != 0 and GSBASE doesn't match the descriptor", so be
it, but this needs to be a conscious decision and needs to be weighed
against the alternatives.
The actual implementation details are just details. They need to
match the intended semantics, of course.
--Andy
next prev parent reply other threads:[~2016-03-21 22:47 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-21 16:16 Updated version of RD/WR FS/GS BASE patchkit Andi Kleen
2016-03-21 16:16 ` [PATCH 1/9] x86: Add intrinsics/macros for new rd/wr fs/gs base instructions Andi Kleen
2016-03-21 18:14 ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 2/9] x86: Add support for rd/wr fs/gs base Andi Kleen
2016-03-21 18:13 ` Andy Lutomirski
2016-03-21 19:05 ` Andi Kleen
2016-03-21 19:22 ` Andy Lutomirski
2016-03-21 22:05 ` Andi Kleen
2016-03-21 22:08 ` Andy Lutomirski
2016-03-21 22:15 ` Andi Kleen
2016-03-22 8:36 ` Thomas Gleixner
2016-03-22 14:40 ` Brian Gerst
2016-04-15 0:06 ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 3/9] x86: Make old K8 swapgs workaround conditional Andi Kleen
2016-03-21 16:16 ` [PATCH 4/9] x86: Enumerate kernel FSGS capability in AT_HWCAP2 Andi Kleen
2016-03-21 18:49 ` Brian Gerst
2016-03-21 18:54 ` Andi Kleen
2016-03-21 19:32 ` Brian Gerst
2016-03-21 19:43 ` Andi Kleen
2016-03-21 22:10 ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 5/9] x86: Add documentation for rd/wr fs/gs base Andi Kleen
2016-03-23 19:14 ` Valdis.Kletnieks
2016-03-21 16:16 ` [PATCH 6/9] x86: Use rd/wr fs/gs base in arch_prctl Andi Kleen
2016-03-21 18:17 ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 7/9] x86: Add self test code for fsgsbase Andi Kleen
2016-03-21 16:16 ` [PATCH 8/9] x86: Support arbitrary fs/gs base in getregs Andi Kleen
2016-03-21 16:16 ` [PATCH 9/9] x86: Save FS/GS base in core dump Andi Kleen
2016-03-21 18:39 ` Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski
2016-03-21 19:03 ` Andi Kleen
2016-03-21 19:23 ` Andy Lutomirski
2016-03-21 19:40 ` Andi Kleen
2016-03-21 22:05 ` Andy Lutomirski
2016-03-21 22:11 ` Andi Kleen
2016-03-21 22:27 ` Andy Lutomirski
2016-03-21 22:41 ` Andi Kleen
2016-03-21 22:47 ` Andy Lutomirski [this message]
2016-03-21 22:52 ` Andi Kleen
2016-03-21 22:57 ` Andy Lutomirski
2016-03-21 23:02 ` Andi Kleen
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