linux-kernel - Re: [PATCH 4/6] x86: fix some bugs about EFI runtime code mapping

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Date:	Fri, 25 Jan 2008 17:26:17 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] x86: fix some bugs about EFI runtime code mapping

On Fri, 2008-01-25 at 10:16 +0100, Ingo Molnar wrote:
> * Huang, Ying <ying.huang@...el.com> wrote:
> 
> > This patch fixes some bugs of making EFI runtime code executable.
> > 
> > - Use change_page_attr in i386 too. Because the runtime code may be
> >   mapped not through ioremap.
> > 
> > - If there is no _PAGE_NX in __supported_pte_mask, the change_page_attr
> >   is not called.
> > 
> > - Make efi_ioremap map pages as PAGE_KERNEL_EXEC, because EFI runtime
> >   code may be mapped through efi_ioremap.
> 
> thanks, applied.
> 
> note that here:
> 
> > -		set_fixmap_nocache(FIX_EFI_IO_MAP_FIRST_PAGE - pages_mapped,
> > -				   offset);
> > +		__set_fixmap(FIX_EFI_IO_MAP_FIRST_PAGE - pages_mapped,
> > +			     offset, PAGE_KERNEL_EXEC);
> 
> you've changed it from nocache-noexec to cached-exec. I suspect that's 
> what we want - except if an early EFI area can be non-prefetchable 
> device memory. Can that ever happen? Would you like to have 
> PAGE_KERNEL_NOCACHE_EXEC perhaps? I implemented that yesterday but did 
> not commit it yet. (see the patch below)

Yes. EFI area can be non-prefetchable device memory. I should use
PAGE_KERNEL_NOCACHE_EXEC.

A question about this:

The MTRR on x86 should have set the memory area as un-cachable. Why do
we bother to set it in page table?

Best Regards,
Huang Ying

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