linux-kernel - Re: [PATCH v5] x86: make sure IDT is page aligned

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Message-ID: <CAE9FiQUrdVW3+FzNhbuubDcZasvsipKwGhsnqxgAmxpVkKryfQ@mail.gmail.com>
Date:	Tue, 16 Jul 2013 16:59:08 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	PaX Team <pageexec@...il.com>
Subject: Re: [PATCH v5] x86: make sure IDT is page aligned

On Tue, Jul 16, 2013 at 4:43 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 07/16/2013 04:39 PM, Yinghai Lu wrote:
>>
>> ok. so the old code is just for optimization to keep it cacheline aligned?
>>
>
> To the best of my knowledge.  I guess I should look through the git log
> to make sure it isn't some old erratum fix.
>
looks like before
commit e57113bc1ff591005ec0b0fb4885d97c01de73d8
Author: Jan Beulich <jbeulich@...ell.com>
Date:   Sat Mar 25 16:30:01 2006 +0100

    [PATCH] x86_64: miscellaneous cleanup

    - adjust limits of GDT/IDT pseudo-descriptors (some were off by one)
    - move empty_zero_page into .bss.page_aligned
    - move cpu_gdt_table into .data.page_aligned
    - move idt_table into .bss
    - align inital_code and init_rsp
    - eliminate pointless (re-)declaration of idt_table in traps.c

it is PAGE aligned as it is after gdt page, after the commit, it is
cacheline aligned.


@@ -378,9 +378,12 @@ gdt_end:
        /* zero the remaining page */
        .fill PAGE_SIZE / 8 - GDT_ENTRIES,8,0

-ENTRY(idt_table)
-       .rept   256
-       .quad   0
-       .quad   0
-       .endr
+       .section .bss, "aw", @nobits
+       .align L1_CACHE_BYTES
+ENTRY(idt_table)
+       .skip 256 * 16

+       .section .bss.page_aligned, "aw", @nobits
+       .align PAGE_SIZE
+ENTRY(empty_zero_page)
+       .skip PAGE_SIZE
--
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