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

[Aneesh Kumar K.V]

On 8/12/20 12:10 PM, Christophe Leroy wrote:
> 
> 
> Le 12/08/2020 à 08:33, Aneesh Kumar K.V a écrit :
>> 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.
>>    */
>>   #define S390_MASK_BITS    4
>> -#define RANDOM_ORVALUE    GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
>> +#define PPC_MASK_BITS    2
>> +#define RANDOM_ORVALUE    GENMASK(BITS_PER_LONG - 1 - PPC_MASK_BITS, 
>> S390_MASK_BITS)
> 
> Do you mean:
> 
> #define RANDOM_ORVALUE    GENMASK(BITS_PER_LONG - 1, PPC_MASK_BITS | 
> S390_MASK_BITS)


IIUC GENMASK(hi, low) generate a mask from hi to low bits. Since i want 
to avoid bit 62, I am forcing it to generate bits from (61, 4)


-aneesh