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Subject: Re: [PATCH] powerpc/mm: Add _PAGE_SAO to _PAGE_CACHE_CTL mask
To: Reza Arbab <arbab@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
References: <1548696702-20686-1-git-send-email-arbab@linux.ibm.com>
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Date: Tue, 29 Jan 2019 20:37:28 +0530
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Cc: Charles Johns <crjohns@us.ibm.com>, Paul Mackerras <paulus@samba.org>
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On 1/28/19 11:01 PM, Reza Arbab wrote:
> In htab_convert_pte_flags(), _PAGE_CACHE_CTL is used to check for the
> _PAGE_SAO flag:
> 
>    else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
>            rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
> 
> But, it isn't defined to include that flag:
> 
>    #define _PAGE_CACHE_CTL (_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> 
> This happens to work, but only because of the flag values:
> 
>    #define _PAGE_SAO               0x00010 /* Strong access order */
>    #define _PAGE_NON_IDEMPOTENT    0x00020 /* non idempotent memory */
>    #define _PAGE_TOLERANT          0x00030 /* tolerant memory, cache inhibited */
> 
> To prevent any issues if these particulars ever change, add _PAGE_SAO to
> the mask.
> 

Not sure what the fix is about. We set the related hash pte flags via

	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_TOLERANT)
		rflags |= HPTE_R_I;
	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_NON_IDEMPOTENT)
		rflags |= (HPTE_R_I | HPTE_R_G);
	else if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
		rflags |= (HPTE_R_W | HPTE_R_I | HPTE_R_M);
	else
		/*
		 * Add memory coherence if cache inhibited is not set
		 */
		rflags |= HPTE_R_M;




> Suggested-by: Charles Johns <crjohns@us.ibm.com>
> Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
> ---
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 2e6ada2..1d97a28 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -811,7 +811,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
>   	return hash__set_pte_at(mm, addr, ptep, pte, percpu);
>   }
>   
> -#define _PAGE_CACHE_CTL	(_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
> +#define _PAGE_CACHE_CTL	(_PAGE_SAO | _PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
>   
>   #define pgprot_noncached pgprot_noncached
>   static inline pgprot_t pgprot_noncached(pgprot_t prot)
>