linux-kernel - Re: -tip tree resume fail, bisect to 5bd5a45(x86: Add NX protection for kernel data)

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Message-ID: <1290421744.4cea45f0614d4@imp.free.fr>
Date:	Mon, 22 Nov 2010 11:29:04 +0100
From:	castet.matthieu@...e.fr
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Matthieu Castet <castet.matthieu@...e.fr>,
	Siarhei Liakh <sliakh.lkml@...il.com>,
	Xuxian Jiang <jiang@...ncsu.edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: -tip tree resume fail, bisect to 5bd5a45(x86: Add NX protection for kernel data)

Hi Andi,

Quoting Andi Kleen <andi@...stfloor.org>:

> On Mon, Nov 22, 2010 at 09:07:10AM +0100, Ingo Molnar wrote:
> > > ---[ High Kernel Mapping ]---
> > > ....
> > > 0xffffffff81a00000-0xffffffff81c00000           2M     ro         PSE GLB
> NX pmd
> > > 0xffffffff81c00000-0xffffffff81d91000        1604K     ro             GLB
> NX pte
> > > 0xffffffff81d91000-0xffffffff81e00000         444K     ro             GLB
> NX pte
> > > 0xffffffff81e00000-0xffffffff82000000           2M     RW         PSE GLB
> NX pmd
> > > 0xffffffff82000000-0xffffffff8200c000          48K     RW             GLB
> NX pte
> > > 0xffffffff8200c000-0xffffffff82100000         976K     RW             GLB
> NX pte
> > > 0xffffffff82100000-0xffffffff82200000           1M     RW             GLB
> NX pte
> > > .....
> > >
> > > The only difference is 0xffffffff81e00000(end) to
> 0xffffffff82200000(kernel_end) is set to NX.
> > >
> > > I guess this range code is used by resume wakeup code. So setting it to
> NX causes problem.
> > >
> > > Any idea?
> >
> > Yeah, the resume area is a trampoline, it needs to be executable.
>
> Also it looks like most of the kernel linker supplied data is now not
> 2MB mapped anymore? That will surely cost TLB entries.
>
Any idea where it comes from ?

The mapping is still not 2MB mapped without the commit.

The patch only add

+#if defined(CONFIG_DEBUG_RODATA)
+	/* .text should occupy whole number of pages */
+	. = ALIGN(PAGE_SIZE);
+#endif
 	X64_ALIGN_DEBUG_RODATA_BEGIN
 	RO_DATA(PAGE_SIZE)
 	X64_ALIGN_DEBUG_RODATA_END

But X64_ALIGN_DEBUG_RODATA_BEGIN is aligned on 2M, so it shouldn't change
nothing on x64 ?

Matthieu
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