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

[Catalin Marinas]

On Mon, Dec 22, 2014 at 03:31:12PM +0000, Catalin Marinas wrote:
> On Mon, Dec 22, 2014 at 03:11:37PM +0000, Jungseok Lee wrote:
> > On Dec 22, 2014, at 9:30 PM, Catalin Marinas wrote:
> > > On Sun, Dec 21, 2014 at 10:56:33AM +0000, Will Deacon wrote:
> > >> On Sat, Dec 20, 2014 at 12:49:40AM +0000, Jungseok Lee wrote:
> > >>> This patch adds pgd_page definition in order to keep supporting
> > >>> HAVE_GENERIC_RCU_GUP configuration. In addition, it changes pud_page
> > >>> expression to align with pmd_page for readability.
> > >>> 
> > >>> An introduction of pgd_page resolves the following build breakage
> > >>> under 4KB + 4Level memory management combo.
> > >>> 
> > >>> mm/gup.c: In function 'gup_huge_pgd':
> > >>> mm/gup.c:889:2: error: implicit declaration of function 'pgd_page' [-Werror=implicit-function-declaration]
> > >>>  head = pgd_page(orig);
> > >>>  ^
> > >>> mm/gup.c:889:7: warning: assignment makes pointer from integer without a cast
> > >>>  head = pgd_page(orig);
> > >>> 
> > >>> Cc: Catalin Marinas <catalin.marinas at arm.com>
> > >>> Cc: Will Deacon <will.deacon at arm.com>
> > >>> Cc: Steve Capper <steve.capper at linaro.org>
> > >>> Signed-off-by: Jungseok Lee <jungseoklee85 at gmail.com>
> > >>> ---
> > >>> arch/arm64/include/asm/pgtable.h | 4 +++-
> > >>> 1 file changed, 3 insertions(+), 1 deletion(-)
> > >>> 
> > >>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > >>> index df22314..a1fe927 100644
> > >>> --- a/arch/arm64/include/asm/pgtable.h
> > >>> +++ b/arch/arm64/include/asm/pgtable.h
> > >>> @@ -401,7 +401,7 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
> > >>> 	return (pmd_t *)pud_page_vaddr(*pud) + pmd_index(addr);
> > >>> }
> > >>> 
> > >>> -#define pud_page(pud)           pmd_page(pud_pmd(pud))
> > >>> +#define pud_page(pud)		pfn_to_page(__phys_to_pfn(pud_val(pud) & PHYS_MASK))
> > >> 
> > >> It would be cleaner to use pud_pfn here, otherwise we end up passing a
> > >> physical address with the lower attributes present to __phys_to_pfn, which
> > >> "knows" to shift them away.
> > > 
> > > It looks like we did the same with pmd_page() but not with pte_page(),
> > > the latter using pte_pfn().
> > > 
> > > It's not a problem with lower attributes because they are within the
> > > first 12 bits, so the shifting gets rid of them. For pmd/pud/pgd, bits
> > > above 12 and up to the actual address must be 0.
> > > 
> > > I agree with changing all of them to use pte/pmd/pud/pgd_pfn but I'm
> > > inclined to merge this patch now to fix the kernel build and we'll look
> > > at the clean-up after Christmas.
> > 
> > Either way, I'm fine.
> 
> Unless you post an updated patch quickly enough ;)

Actually, don't worry, I'll fold Will's suggestions into your patch. I
found another problem with pmd_page being defined twice.

Thanks.

-- 
Catalin