linux-kernel - Re: [PATCH 00 of 10] x86: unify asm/pgtable.h

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Date:	Tue, 08 Jan 2008 19:22:46 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <ak@...e.de>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	Jan Beulich <jbeulich@...ell.com>
Subject: Re: [PATCH 00 of 10] x86: unify asm/pgtable.h

Andi Kleen wrote:
>> Yeah, that may be true, but this particular tree is weird, and I'm trying 
>> to understand what's going on here.  Specifically, 64-bit ioremap()s 
>> *don't* set _PAGE_GLOBAL, which appears to be an accident resulting from 
>> the strange definitions of __PAGE_KERNEL_* vs PAGE_KERNEL_*. 
>>     
>
> ioremap() should set G agreed.
>
>   
>> For example, ioremap_64.c:__ioremap() creates a vma for the io mapping, and 
>> explicitly sets _PAGE_GLOBAL in the vma's version of pgprot - but then it 
>> calls ioremap_page_range() to actually create the mapping, which ends up 
>> making a non-global mapping, because its rolling its own version of 
>> PAGE_KERNEL by using pgprot(__PAGE_KERNEL) - which is not the actual 
>> definition of PAGE_KERNEL.
>>     
>
> That should not really matter because ioremap_change_attr()->c_p_a is only called
> when flags is != 0 and that means it is already different from PAGE_KERNEL.
>
>   
>> I think there's a bug around here, but I think its currently being hidden 
>>     
>
> There's one Jan pointed out: iounmap does not subtract the guard page size
> so it ends up resetting one page too much. That is probably what causes your
> problem. But again you should be passing in G in the first place.
>
> -Andi
>
> Here was Jan's patch; it incidently fixes the G problem too
>   

OK, great.  Ingo, that means we can use this and go back to folding 
_PAGE_GLOBAL into __PAGE_KERNEL_*.  Well, at least give it a try.

    J

> snip
>
> Additionally I found it necessary to fix ioremap_64.c's use of
> change_page_attr_addr():
>
> --- a/arch/x86/mm/ioremap_64.c
> +++ b/arch/x86/mm/ioremap_64.c
> @@ -48,7 +48,7 @@ ioremap_change_attr(unsigned long phys_a
>   		 * Must use a address here and not struct page because the phys addr
>  		 * can be a in hole between nodes and not have an memmap entry.
>  		 */
> -		err = change_page_attr_addr(vaddr,npages,__pgprot(__PAGE_KERNEL|flags));
> +		err = change_page_attr_addr(vaddr,npages,MAKE_GLOBAL(__PAGE_KERNEL|flags));
>  		if (!err)
>  			global_flush_tlb();
>  	}
> @@ -199,7 +199,7 @@ void iounmap(volatile void __iomem *addr
>  
>  	/* Reset the direct mapping. Can block */
>  	if (p->flags >> 20)
> -		ioremap_change_attr(p->phys_addr, p->size, 0);
> +		ioremap_change_attr(p->phys_addr, get_vm_area_size(p), 0);
>  
>  	/* Finally remove it */
>  	o = remove_vm_area((void *)addr);
>
> Other extra changes I had in my version could possibly be counted as enhancements...
>
> Jan
>   

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