From: Anshuman Khandual <anshuman.khandual@arm.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
linux-mm@kvack.org, akpm@linux-foundation.org
Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org,
linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org,
linux-snps-arc@lists.infradead.org, x86@kernel.org,
linux-arch@vger.kernel.org,
Gerald Schaefer <gerald.schaefer@de.ibm.com>,
Christophe Leroy <christophe.leroy@c-s.fr>,
Vineet Gupta <vgupta@synopsys.com>,
Mike Rapoport <rppt@linux.ibm.com>, Qian Cai <cai@lca.pw>
Subject: Re: [PATCH v3 03/13] mm/debug_vm_pgtable/ppc64: Avoid setting top bits in radom value
Date: Wed, 2 Sep 2020 09:15:12 +0530 [thread overview]
Message-ID: <2f6f2e26-5c77-d9cb-667c-0f7d35923e31@arm.com> (raw)
In-Reply-To: <3f20130a-f9fc-db9d-50a9-76aca5a1a6d7@linux.ibm.com>
On 09/01/2020 01:25 PM, Aneesh Kumar K.V wrote:
> On 9/1/20 1:16 PM, Anshuman Khandual wrote:
>>
>>
>> On 09/01/2020 01:06 PM, Aneesh Kumar K.V wrote:
>>> 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@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.
>>
>> Thats okay as long it does not adversely affect other architectures, ignoring
>> some more bits is acceptable. Like existing S390_MASK_BITS gets ignored on all
>> other platforms even if it is a s390 specific constraint. Not having platform
>> specific #ifdef here, is essential.
>>
>
> Why is it essential?
IIRC, I might have already replied on this couple of times. But let me try once more.
It is a generic test aimed at finding inconsistencies between different architectures
in terms of the page table helper semantics. Any platform specific construct here, to
'make things work' has the potential to hide such inconsistencies and defeat the very
purpose. The test/file here follows this rule consistently i.e there is not a single
platform specific #ifdef right now and would really like to continue maintaining this
property, unless until absolutely necessary. Current situation here wrt 32 bit archs
can easily be accommodated with a generic check such as __BITS_PER_LONG.
next prev parent reply other threads:[~2020-09-02 3:46 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-27 8:04 [PATCH v3 00/13] mm/debug_vm_pgtable fixes Aneesh Kumar K.V
2020-08-27 8:04 ` [PATCH v3 01/13] powerpc/mm: Add DEBUG_VM WARN for pmd_clear Aneesh Kumar K.V
2020-09-01 3:12 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 02/13] powerpc/mm: Move setting pte specific flags to pfn_pte Aneesh Kumar K.V
2020-09-01 3:13 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 03/13] mm/debug_vm_pgtable/ppc64: Avoid setting top bits in radom value Aneesh Kumar K.V
2020-09-01 3:15 ` Anshuman Khandual
2020-09-01 6:21 ` Aneesh Kumar K.V
2020-09-01 7:32 ` Anshuman Khandual
2020-09-01 7:36 ` Aneesh Kumar K.V
2020-09-01 7:46 ` Anshuman Khandual
2020-09-01 7:55 ` Aneesh Kumar K.V
2020-09-02 3:45 ` Anshuman Khandual [this message]
2020-08-27 8:04 ` [PATCH v3 04/13] mm/debug_vm_pgtables/hugevmap: Use the arch helper to identify huge vmap support Aneesh Kumar K.V
2020-09-01 3:16 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 05/13] mm/debug_vm_pgtable/savedwrite: Enable savedwrite test with CONFIG_NUMA_BALANCING Aneesh Kumar K.V
2020-09-01 3:18 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 06/13] mm/debug_vm_pgtable/THP: Mark the pte entry huge before using set_pmd/pud_at Aneesh Kumar K.V
2020-09-01 3:21 ` Anshuman Khandual
2020-09-01 6:23 ` Aneesh Kumar K.V
2020-08-27 8:04 ` [PATCH v3 07/13] mm/debug_vm_pgtable/set_pte/pmd/pud: Don't use set_*_at to update an existing pte entry Aneesh Kumar K.V
2020-08-27 8:04 ` [PATCH v3 08/13] mm/debug_vm_pgtable/thp: Use page table depost/withdraw with THP Aneesh Kumar K.V
2020-09-01 3:22 ` Anshuman Khandual
2020-09-01 6:25 ` Aneesh Kumar K.V
2020-09-01 6:50 ` Christophe Leroy
2020-09-01 7:40 ` Aneesh Kumar K.V
2020-09-01 7:51 ` Christophe Leroy
2020-09-02 3:45 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 09/13] mm/debug_vm_pgtable/locks: Move non page table modifying test together Aneesh Kumar K.V
2020-09-01 3:41 ` Anshuman Khandual
2020-09-01 6:38 ` Aneesh Kumar K.V
2020-09-01 9:33 ` Anshuman Khandual
2020-09-01 9:36 ` Aneesh Kumar K.V
2020-09-01 9:58 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 10/13] mm/debug_vm_pgtable/locks: Take correct page table lock Aneesh Kumar K.V
2020-09-01 3:44 ` Anshuman Khandual
2020-08-27 8:04 ` [PATCH v3 11/13] mm/debug_vm_pgtable/pmd_clear: Don't use pmd/pud_clear on pte entries Aneesh Kumar K.V
2020-08-27 8:04 ` [PATCH v3 12/13] mm/debug_vm_pgtable/hugetlb: Disable hugetlb test on ppc64 Aneesh Kumar K.V
2020-09-01 4:03 ` Anshuman Khandual
2020-09-01 6:30 ` Aneesh Kumar K.V
2020-09-01 7:59 ` Christophe Leroy
2020-09-02 13:05 ` Anshuman Khandual
2020-09-02 13:20 ` Aneesh Kumar K.V
2020-08-27 8:04 ` [PATCH v3 13/13] mm/debug_vm_pgtable: populate a pte entry before fetching it Aneesh Kumar K.V
2020-08-27 12:17 ` kernel test robot
2020-09-01 3:25 ` Anshuman Khandual
2020-09-01 6:37 ` Aneesh Kumar K.V
2020-09-01 7:38 ` Anshuman Khandual
2020-09-01 9:58 ` Aneesh Kumar K.V
2020-09-02 3:49 ` Anshuman Khandual
2020-09-02 3:58 ` Aneesh Kumar K.V
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