Fwd: [Bug 213069] New: kernel BUG at arch/powerpc/include/asm/book3s/64/hash-4k.h:147! Oops: Exception in kernel mode, sig: 5 [#1]

[Anshuman Khandual]

On 5/17/21 6:29 PM, Christophe Leroy wrote:
> 
> 
> Le 17/05/2021 à 14:49, Anshuman Khandual a écrit :
>>
>>
>> On 5/17/21 11:25 AM, Aneesh Kumar K.V wrote:
>>> On 5/17/21 11:17 AM, Christophe Leroy wrote:
>>>> +aneesh
>>>> +linuxppc-dev list
>>>>
>>>> Le 17/05/2021 à 07:44, Anshuman Khandual a écrit :
>>>>> Hello Christophe,
>>>>>
>>>>> DEBUG_VM_PGTABLE has now been re-enabled on powerpc recently ? was not
>>>>> aware about this. From the error log, it failed explicitly on 4K page
>>>>> size hash config.
>>>>>
>>>>> static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
>>>>> {
>>>>>           BUG();        ------> Failed
>>>>>           return pmd;
>>>>> }
>>>>>
>>>>> static inline pmd_t __pmd_mkhuge(pmd_t pmd)
>>>>> {
>>>>>           if (radix_enabled())
>>>>>                   return radix__pmd_mkhuge(pmd);
>>>>>           return hash__pmd_mkhuge(pmd);
>>>>> }
>>>>>
>>>>> pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot)
>>>>> {
>>>>>           unsigned long pmdv;
>>>>>
>>>>>           pmdv = (pfn << PAGE_SHIFT) & PTE_RPN_MASK;
>>>>>
>>>>>           return __pmd_mkhuge(pmd_set_protbits(__pmd(pmdv), pgprot));
>>>>> }
>>>>>
>>>>> It seems like on powerpc, where pfn_pmd() makes a huge page but which
>>>>> is not supported on 4K hash config thus triggering the BUG(). But all
>>>>> pfn_pmd() call sites inside the debug_vm_pgtable() test are protected
>>>>> with CONFIG_TRANSPARENT_HUGEPAGE. IIUC unlike powerpc, pfn_pmd() does
>>>>> not directly make a huge page on other platforms.
>>>>>
>>>>> Looking at arch/powerpc/include/asm/book3s/64/hash-4k.h, all relevant
>>>>> THP helpers has BUG() or 0 which indicates THP might not be supported
>>>>> on 4K page size hash config ?
>>>>>
>>>>> But looking at arch/powerpc/platforms/Kconfig.cputype, it seems like
>>>>> HAVE_ARCH_TRANSPARENT_HUGEPAGE is invariably selected on PPC_BOOK3S_64
>>>>> platforms which I assume includes 4K page size hash config as well.
>>>>>
>>>>> Is THP some how getting enabled on this 4K page size hash config where
>>>>> it should not be (thus triggering the BUG) ? OR am I missing something
>>>>> here.
>>>>>
>>>>
>>>
>>> We should put those  pfn_pmd()  and pfn_pud() after
>>>
>>>      if (!has_transparent_hugepage())
>>>          return;
>>
>> The following patch has been lightly tested on arm64 and x86 platforms.
>> Could you please verify if this solves the problem on powerpc 4K hash
>> config ? Thank you.
> 
> No need to update pmd_advanced_tests() and pud_advanced_tests() ?

They already have has_transparent_hugepage() check and all pfn_pxx()
instances are after that check. Do you see any other concern ?

> 
> Christophe