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Date:   Mon, 15 Jun 2020 15:22:44 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 3/3] powerpc/8xx: Provide ptep_get() with 16k pages
Message-ID: <20200615132244.GR2531@hirez.programming.kicks-ass.net>
References: <cover.1592225557.git.christophe.leroy@csgroup.eu>
 <341688399c1b102756046d19ea6ce39db1ae4742.1592225558.git.christophe.leroy@csgroup.eu>
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On Mon, Jun 15, 2020 at 12:57:59PM +0000, Christophe Leroy wrote:
> READ_ONCE() now enforces atomic read, which leads to:


> Fixes: 2ab3a0a02905 ("READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses")
> Cc: Will Deacon <will@kernel.org>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/include/asm/nohash/32/pgtable.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/nohash/32/pgtable.h b/arch/powerpc/include/asm/nohash/32/pgtable.h
> index b56f14160ae5..77addb599ce7 100644
> --- a/arch/powerpc/include/asm/nohash/32/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/32/pgtable.h
> @@ -286,6 +286,16 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
>  	return __pte(pte_update(mm, addr, ptep, ~0, 0, 0));
>  }
>  
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> +#define __HAVE_ARCH_PTEP_GET
> +static inline pte_t ptep_get(pte_t *ptep)
> +{
> +	pte_t pte = {READ_ONCE(ptep->pte), 0, 0, 0};
> +
> +	return pte;
> +}
> +#endif

Would it make sense to have a comment with this magic? The casual reader
might wonder WTH just happened when he stumbles on this :-)

Other than that, the series looks good to me, Thanks!

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>