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

Jeremy Fitzhardinge
2008-01-09T03:24:44Z

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
>