[PATCH] arm64: Fix THP protection change logic

[Catalin Marinas]

On Thu, Oct 01, 2015 at 01:06:07PM +0100, Steve Capper wrote:
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 56283f8..cf73194 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -80,7 +80,7 @@ extern void __pgd_error(const char *file, int line, unsigned long val);
>  #define PAGE_S2			__pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY)
>  #define PAGE_S2_DEVICE		__pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDONLY | PTE_UXN)
>  
> -#define PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
> +#define PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_VALID) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
>  #define PAGE_SHARED		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
>  #define PAGE_SHARED_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
>  #define PAGE_COPY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
> @@ -460,7 +460,7 @@ static inline pud_t *pud_offset(pgd_t *pgd, unsigned long addr)
>  static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>  {
>  	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
> -			      PTE_PROT_NONE | PTE_WRITE | PTE_TYPE_MASK;
> +			      PTE_PROT_NONE | PTE_VALID | PTE_WRITE;
>  	pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
>  	return pte;
>  }

Thanks for looking into this. So for ptes, we need the type bits to be:

0b?0: unmapped/PAGE_NONE
0b11: mapped

With pmd block (huge page), we want:

0b?0: unmapped/PAGE_NONE
0b01: mapped

With your fix, bit 1 is no longer touched by pte_modify(). It looks fine
to me. Another option would have been a separate pmd_modify() function
with its own mask but I think it's cleaner this way.

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>

Let's see if it fixes the issue for Ganapatrao and Will or I will send
it upstream.

-- 
Catalin