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Subject: Re: [PATCH v4 03/13] mm/debug_vm_pgtable/ppc64: Avoid setting top
 bits in radom value
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, linux-mm@kvack.org,
 akpm@linux-foundation.org
References: <20200902114222.181353-1-aneesh.kumar@linux.ibm.com>
 <20200902114222.181353-4-aneesh.kumar@linux.ibm.com>
From: Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <74b87dca-1c8d-6458-8af6-392b87c0bfc6@arm.com>
Date: Fri, 4 Sep 2020 09:33:47 +0530
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On 09/02/2020 05:12 PM, Aneesh Kumar K.V wrote:
> ppc64 use bit 62 to indicate a pte entry (_PAGE_PTE). Avoid setting
> that bit in random value.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  mm/debug_vm_pgtable.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 086309fb9b6f..00649b47f6e0 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -44,10 +44,17 @@
>   * entry type. But these bits might affect the ability to clear entries with
>   * pxx_clear() because of how dynamic page table folding works on s390. So
>   * while loading up the entries do not change the lower 4 bits. It does not
> - * have affect any other platform.
> + * have affect any other platform. Also avoid the 62nd bit on ppc64 that is
> + * used to mark a pte entry.
>   */
> -#define S390_MASK_BITS	4
> -#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
> +#define S390_SKIP_MASK		GENMASK(3, 0)
> +#if __BITS_PER_LONG == 64
> +#define PPC64_SKIP_MASK		GENMASK(62, 62)
> +#else
> +#define PPC64_SKIP_MASK		0x0
> +#endif
> +#define ARCH_SKIP_MASK (S390_SKIP_MASK | PPC64_SKIP_MASK)
> +#define RANDOM_ORVALUE (GENMASK(BITS_PER_LONG - 1, 0) & ~ARCH_SKIP_MASK)
>  #define RANDOM_NZVALUE	GENMASK(7, 0)
>  
>  static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
> 

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>