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From: "Bae, Chang Seok" <chang.seok.bae@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"Metzger, Markus T" <markus.t.metzger@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: RE: [regression in -rc1] Re: [PATCH v6 2/8] x86/fsgsbase/64: Introduce FS/GS base helper functions
Date: Wed, 24 Oct 2018 19:13:32 +0000	[thread overview]
Message-ID: <C9BB696F3A938947B10DCAD29FAB8FFA66CCBBE3@CRSMSX101.amr.corp.intel.com> (raw)
In-Reply-To: <CALCETrUr3DGwW8y6y_cffEKWO_KQs1J2_UvTBZsbdAzES_f-Ag@mail.gmail.com>

On Tue, Sep 18, 2018 at 12:02 PM Andy Lutomirski <luto@kernel.org>
> On Tue, Sep 18, 2018 at 4:09 PM Chang S. Bae <chang.seok.bae@intel.com>
> wrote:
> >
> > With new helpers, FS/GS base access is centralized.
> > Eventually, when FSGSBASE instruction enabled, it will be faster.
> 
> Sorry for not catching this during review, but:
> 
> > +void x86_fsbase_write_cpu(unsigned long fsbase) {
> > +       /*
> > +        * Set the selector to 0 as a notion, that the segment base is
> > +        * overwritten, which will be checked for skipping the segment load
> > +        * during context switch.
> > +        */
> > +       loadseg(FS, 0);
> 
> ^^^
> 
> what?
> 
> > +       wrmsrl(MSR_FS_BASE, fsbase);
> > +}
> 
> I don't understand what the comment is trying to say, but the sole caller so far
> of this function is x86_gsbase_write_task(), and the code looks incorrect.
> 
> Ingo, I think we need to address this during this merge window, probably by
> removing the comment and the loadseg() call (and the same for
> gsbase...inactive).  But first, Chang, can you explain what exactly your intent is
> here?

It's coming from do_arch_prctl_64(). If you think it really makes confusion in 
x86_fsbase_write_cpu(), how about moving it to x86_fsbase_write_task()?

Chang

  reply	other threads:[~2018-10-24 19:13 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-18 23:08 [PATCH v6 0/8] x86: infrastructure to enable FSGSBASE Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 1/8] x86/arch_prctl/64: Make ptrace read FS/GS base accurately Chang S. Bae
2018-10-08  9:54   ` [tip:x86/asm] x86/fsgsbase/64: Fix ptrace() to read the " tip-bot for Andy Lutomirski
2018-10-08  9:59   ` [tip:x86/asm] x86/segments: Introduce the 'CPUNODE' naming to better document the segment limit CPU/node NR trick tip-bot for Ingo Molnar
2018-10-08  9:59   ` [tip:x86/asm] x86/fsgsbase/64: Clean up various details tip-bot for Ingo Molnar
2018-09-18 23:08 ` [PATCH v6 2/8] x86/fsgsbase/64: Introduce FS/GS base helper functions Chang S. Bae
2018-10-08  9:55   ` [tip:x86/asm] " tip-bot for Chang S. Bae
2018-10-24 19:01   ` [regression in -rc1] Re: [PATCH v6 2/8] " Andy Lutomirski
2018-10-24 19:13     ` Bae, Chang Seok [this message]
2018-10-24 19:22       ` Andy Lutomirski
2018-10-24 19:29         ` Bae, Chang Seok
2018-10-24 19:43           ` Andy Lutomirski
2018-10-24 22:50             ` Bae, Chang Seok
2018-10-25 22:37     ` Andy Lutomirski
2018-09-18 23:08 ` [PATCH v6 3/8] x86/fsgsbase/64: Make ptrace use correct FS/GS base helpers Chang S. Bae
2018-10-08  9:56   ` [tip:x86/asm] x86/fsgsbase/64: Make ptrace use the new " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 4/8] x86/fsgsbase/64: Use FS/GS base helpers in core dump Chang S. Bae
2018-10-08  9:56   ` [tip:x86/asm] x86/fsgsbase/64: Convert the ELF core dump code to the new FSGSBASE helpers tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 5/8] x86/fsgsbase/64: Factor out load FS/GS segments from __switch_to() Chang S. Bae
2018-10-08  9:57   ` [tip:x86/asm] x86/fsgsbase/64: Factor out FS/GS segment loading " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 6/8] x86/segments/64: Rename PER_CPU segment to CPU_NUMBER Chang S. Bae
2018-10-08  9:57   ` [tip:x86/asm] x86/segments/64: Rename the GDT PER_CPU entry " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 7/8] x86/vdso: Introduce helper functions for CPU and node number Chang S. Bae
2018-10-08  9:58   ` [tip:x86/asm] " tip-bot for Chang S. Bae
2018-09-18 23:08 ` [PATCH v6 8/8] x86/vdso: Move out the CPU initialization Chang S. Bae
2018-10-08  8:36   ` Ingo Molnar
2018-10-08  9:58   ` [tip:x86/asm] x86/vdso: Initialize the CPU/node NR segment descriptor earlier tip-bot for Chang S. Bae

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