[PATCH] arm64: mm: Add pgd_page to support RCU fast_gup

[Jungseok Lee]

On Dec 24, 2014, at 1:01 AM, Catalin Marinas wrote:
> On Tue, Dec 23, 2014 at 03:37:14PM +0000, Jungseok Lee wrote:
>> It looks like that pmd_page cannot be written using pmd_pfn unless pmd_pfn is
>> changed since pmd_pfn masks an input value with PMD_MASK, but pmd_page does not.
>> Additionally, I'm not sure about whether pmd_pfn with PMD_MASK works well for an
>> user process page table.
>> 
>> So, my change on pmd_pfn and pmd_page is as follows. Please correct me if I am wrong.
>> 
>> -----8<-----
>> 
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -294,11 +294,11 @@ void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
>> 
>> #define pmd_mkhuge(pmd)                (__pmd(pmd_val(pmd) & ~PMD_TABLE_BIT))
>> 
>> -#define pmd_pfn(pmd)           (((pmd_val(pmd) & PMD_MASK) & PHYS_MASK) >> PAGE_SHIFT)
>> +#define pmd_pfn(pmd)           ((pmd_val(pmd) & PHYS_MASK) >> PAGE_SHIFT)
>> #define pfn_pmd(pfn,prot)      (__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
>> #define mk_pmd(page,prot)      pfn_pmd(page_to_pfn(page),prot)
>> 
>> -#define pmd_page(pmd)           pfn_to_page(__phys_to_pfn(pmd_val(pmd) & PHYS_MASK))
>> +#define pmd_page(pmd)          pfn_to_page(pmd_pfn(pmd))
>> #define pud_write(pud)         pte_write(pud_pte(pud))
>> #define pud_pfn(pud)           (((pud_val(pud) & PUD_MASK) & PHYS_MASK) >> PAGE_SHIFT)
> 
> It looks like pmd_pfn() is only used for huge pages, so the original
> code was safe. As I said, I won't do further changes here, at least not
> for 3.19.

Okay, everything is clear.

Best Regards
Jungseok Lee