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From: Andy Lutomirski <luto@amacapital.net>
To: Andi Kleen <andi@firstfloor.org>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>
Subject: Re: [PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G optimization
Date: Tue, 26 Apr 2016 15:33:30 -0700	[thread overview]
Message-ID: <CALCETrU_ipRP6baNTpCjrAXvhhk7=8oWzZzvwTqkJc4JrMBJZA@mail.gmail.com> (raw)
In-Reply-To: <20160426205030.GI13997@two.firstfloor.org>

On Tue, Apr 26, 2016 at 1:50 PM, Andi Kleen <andi@firstfloor.org> wrote:
> On Tue, Apr 26, 2016 at 12:23:28PM -0700, Andy Lutomirski wrote:
>> As far as I know, the optimization doesn't work on any modern distro
>> because modern distros use high addresses for ASLR.  Remove it.
>
> I disagree with this patch. For example it will be a regression
> for static executables.  And randomly making old systems slower is a bad
> idea.

That's odd.  statically linked glibc uses low addresses, even in PIE
mode.  I wonder why.

In any event, this isn't actually much of a performance regression, it
has no effect on normal dynamically linked programs, and it's a
considerably simplification, so I still think it's a good idea.  It
also removes some nasty special cases from code that is already way
too full of special cases for comfort.

--Andy

  reply	other threads:[~2016-04-26 22:33 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-26 19:23 [PATCH 0/8] x86: A round of x86 segmentation improvements Andy Lutomirski
2016-04-26 19:23 ` [PATCH 1/8] x86/asm: Stop depending on ptrace.h in alternative.h Andy Lutomirski
2016-04-29 10:48   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 2/8] x86/asm: Make asm/alternative.h safe from assembly Andy Lutomirski
2016-04-29 10:49   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 3/8] x86/segments/64: When loadsegment(fs, ...) fails, clear the base Andy Lutomirski
2016-04-29 10:49   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 4/8] x86/segments/64: When load_gs_index " Andy Lutomirski
2016-04-29 10:49   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 5/8] x86/arch_prctl/64: Remove FSBASE/GSBASE < 4G optimization Andy Lutomirski
2016-04-26 20:50   ` Andi Kleen
2016-04-26 22:33     ` Andy Lutomirski [this message]
2016-04-29 10:50   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 6/8] x86/asm/64: Rename thread_struct's fs and gs to fsbase and gsbase Andy Lutomirski
2016-04-29 10:50   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 7/8] x86/tls: Synchronize segment registers in set_thread_area Andy Lutomirski
2016-04-29 10:51   ` [tip:x86/asm] x86/tls: Synchronize segment registers in set_thread_area() tip-bot for Andy Lutomirski
2016-04-26 19:23 ` [PATCH 8/8] selftests/x86/ldt_gdt: Test set_thread_area deletion of an active segment Andy Lutomirski
2016-04-29 10:51   ` [tip:x86/asm] selftests/x86/ldt_gdt: Test set_thread_area() " tip-bot for Andy Lutomirski

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