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

[castet.matthieu@free.fr]

Hi Andi,

Quoting Andi Kleen <andi@firstfloor.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