linux-kernel - Re: [PATCH] Fix left over EFI cache mapping problems

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Date:	Fri, 15 Feb 2008 15:32:40 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>, torvalds@...l.org,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix left over EFI cache mapping problems

On Fri, 2008-02-15 at 08:08 +0100, Ingo Molnar wrote:
> * Huang, Ying <ying.huang@...el.com> wrote:
> 
> > On Thu, 2008-02-14 at 17:12 +0100, Ingo Molnar wrote: 
> > > this is indeed a bug (we change the attributes for a larger area than 
> > > needed), but your fix is unclean. Find below a cleaner solution.
> > > 
> > > Ying, if you agree with this fix could you please test and ACK it before 
> > > we push it to Linus? (this fix is also in the latest x86.git#mm)
> > 
> > I think the patch following may be better, because it is possible that 
> > the EFI_PAGE_SHIFT and PAGE_SHIFT are different.
> 
> right now, EFI page size is 4096:
> 
>   include/linux/efi.h:#define EFI_PAGE_SHIFT          12
> 
> i doubt we'll ever change PAGE_SIZE on x86 - ia64's variable lowlevel 
> pagesizes are not particularly useful IMO. I think we'll at most have 
> some generic kernel feature that allows a larger PAGE_CACHE_SHIFT - but 
> on the lowlevel MMU level we'll always stay at 4K.
> 
> and i doubt EFI_PAGE_SHIFT would want to (ever) go away from 12 either. 

Yes. I think so too.

> So perhaps, at least as far as arch/x86/kernel/efi*.c files go, it would 
> be cleaner to just replace EFI_PAGE_SHIFT with PAGE_SHIFT and 
> EFI_PAGE_SIZE with PAGE_SIZE?

Maybe. On x86, the only usage of EFI memory map (and
EFI_PAGE_SHIFT/EFI_PAGE_SIZE) is to map the EFI runtime memory area. So
I think either dealing with potential difference now or doing it in the
future when necessary is easy.

Best Regards,
Huang Ying

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