From: Andy Lutomirski <luto@kernel.org>
To: "Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc: Andrew Lutomirski <luto@kernel.org>,
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>,
"Ravi V. Shankar" <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 12:22:22 -0700 [thread overview]
Message-ID: <CALCETrWMMQDa4T0m34GfkkYBxqwGUOg96aeWgiANRv9tCvQVRw@mail.gmail.com> (raw)
In-Reply-To: <C9BB696F3A938947B10DCAD29FAB8FFA66CCBBE3@CRSMSX101.amr.corp.intel.com>
On Wed, Oct 24, 2018 at 12:13 PM Bae, Chang Seok
<chang.seok.bae@intel.com> wrote:
>
> 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()?
Why should ..write_task() magically change the index but only if it's
writing current?
I think you should move it all the way out to the caller
(do_arch_prctl_64()?) and we can see if it makes sense there.
>
> Chang
next prev parent reply other threads:[~2018-10-24 19:22 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
2018-10-24 19:22 ` Andy Lutomirski [this message]
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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