Subject: Re: [PATCH v2] powerpc/mm: Check for _PAGE_PTE in *_devmap()

From: [email-masked]
Date: Thu, 27 Jul 2017 18:47:21 -0300

On Fri, Jul 28, 2017 at 01:35:53AM +1000, Oliver O'Halloran wrote:
> The ISA radix translation tree contains two different types of entry,
> directories and leaves. The formats of the two entries are different
> with the directory entries containing no spare bits for use by software.
> As a result we need to ensure that the *_devmap() family of functions
> check fail for everything except leaf (PTE) entries.
> 
> Signed-off-by: Oliver O'Halloran <[email-masked]>
> ---
> "i'll just tweak the mbox before i sent it, what's the worst that can happen"
> *completely breaks KVM*
> "..."
> ---
>  arch/powerpc/include/asm/book3s/64/pgtable.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index d1da415..6bc6248 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -610,7 +610,9 @@ static inline pte_t pte_mkdevmap(pte_t pte)
> 
>  static inline int pte_devmap(pte_t pte)
>  {
> -	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_DEVMAP));
> +	uint64_t mask = cpu_to_be64(_PAGE_DEVMAP | _PAGE_PTE);
> +
> +	return (pte_raw(pte) & mask) == mask;
>  }
> 
>  static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
> -- 
> 2.7.4
> 

Michael should thank you because I was about to send another insane
suggestion and ask him if that makes sense. :-D

Tested-by: Jose Ricardo Ziviani <[email-masked]>