[PATCH v3 03/13] mm/debug_vm_pgtable/ppc64: Avoid setting top bits in radom value

[Aneesh Kumar K.V]

On 9/1/20 1:02 PM, Anshuman Khandual wrote:
> 
> 
> On 09/01/2020 11:51 AM, Aneesh Kumar K.V wrote:
>> On 9/1/20 8:45 AM, Anshuman Khandual wrote:
>>>
>>>
>>> On 08/27/2020 01:34 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 | 13 ++++++++++---
>>>>    1 file changed, 10 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>>> index 086309fb9b6f..bbf9df0e64c6 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)
>>>> +#ifdef CONFIG_PPC_BOOK3S_64
>>>> +#define PPC64_SKIP_MASK        GENMASK(62, 62)
>>>> +#else
>>>> +#define PPC64_SKIP_MASK        0x0
>>>> +#endif
>>>
>>> Please drop the #ifdef CONFIG_PPC_BOOK3S_64 here. We already accommodate skip
>>> bits for a s390 platform requirement and can also do so for ppc64 as well. As
>>> mentioned before, please avoid adding any platform specific constructs in the
>>> test.
>>>
>>
>>
>> that is needed so that it can be built on 32 bit architectures.I did face build errors with arch-linux
> 
> Could not (#if __BITS_PER_LONG == 32) be used instead or something like
> that. But should be a generic conditional check identifying 32 bit arch
> not anything platform specific.
> 

that _PAGE_PTE bit is pretty much specific to PPC BOOK3S_64.  Not sure 
why other architectures need to bothered about ignoring bit 62.

-aneesh