[PATCH 02/16] debug_vm_pgtable/ppc64: Avoid setting top bits in radom value

[Aneesh Kumar K.V]

On 8/12/20 1:42 PM, Anshuman Khandual wrote:
> 
> 
> On 08/12/2020 12:03 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 at linux.ibm.com>
>> ---
>>   mm/debug_vm_pgtable.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index 086309fb9b6f..4c32063a8acf 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -45,9 +45,12 @@
>>    * 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.
>> + *
>> + * Also avoid the 62nd bit on ppc64 that is used to mark a pte entry.
>>    */
> 
> Please move and fold the above line with the existing paragraph.
> 
>>   #define S390_MASK_BITS	4
>> -#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
>> +#define PPC_MASK_BITS	2
> 
> s/PPC/PPC64/
> 
>> +#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1 - PPC_MASK_BITS, S390_MASK_BITS)
>>   #define RANDOM_NZVALUE	GENMASK(7, 0)
>>   
>>   static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
>>
> 
> With this change, RANDOM_ORVALUE will be (0x3ffffffffffffff0) which discards
> both bit 63 and 62. If only bit 62 is to be avoided for ppc64 the mask should
> be (0xbffffffffffffff0) instead. The following change on this patch should do
> the trick.
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index eb059fef89c2..1499181fb0e9 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -45,13 +45,13 @@
>    * 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.
> - *
> - * Also avoid the 62nd bit on ppc64 that is used to mark a pte entry.
> + * 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 PPC_MASK_BITS  2
> -#define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1 - PPC_MASK_BITS, S390_MASK_BITS)
> +#define S390_SKIP_MASK GENMASK(3, 0)
> +#define PPC64_SKIP_MASK        GENMASK(62, 62)
> +#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)
> 

I will switch to this.

-aneesh