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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: 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]
Date: Mon, 17 May 2021 11:25:35 +0530	[thread overview]
Message-ID: <e9558e0a-314e-ddfd-6776-84c1bfe6f01f@linux.ibm.com> (raw)
In-Reply-To: <7ebc28ad-61e3-ef43-d670-9b80a61268c4@csgroup.eu>

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;


On hash with 4K page size, we can't support leaf page table entry and 
PMD and PUD level. Hence we don't support THP for them.

-aneesh

  reply	other threads:[~2021-05-17  5:56 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-14 23:44 bugzilla-daemon
2021-05-15 10:20 ` [Bug 213069] " bugzilla-daemon
     [not found] ` <4deb5cd5-c713-b020-9143-c74a031e3fd5@csgroup.eu>
     [not found]   ` <a8841b4e-3bff-f600-eac7-501f78ced54b@arm.com>
2021-05-17  5:47     ` Fwd: [Bug 213069] New: " Christophe Leroy
2021-05-17  5:55       ` Aneesh Kumar K.V [this message]
2021-05-17  7:25         ` Anshuman Khandual
2021-05-17  7:44           ` Aneesh Kumar K.V
2021-05-17 10:53             ` Anshuman Khandual
2021-05-17 11:14               ` Aneesh Kumar K.V
2021-05-17 12:49         ` Anshuman Khandual
2021-05-17 12:59           ` Christophe Leroy
2021-05-17 13:12             ` Anshuman Khandual
2021-05-17 15:26               ` Christophe Leroy
2021-05-17 13:52           ` Aneesh Kumar K.V
2021-05-17 14:12             ` Anshuman Khandual
2021-05-17  6:21 ` [Bug 213069] " bugzilla-daemon
2021-05-17 10:36 ` bugzilla-daemon
2021-05-17 12:57 ` bugzilla-daemon
2021-05-19  1:56 ` bugzilla-daemon
2021-06-04  0:36 ` bugzilla-daemon
2021-06-18 23:18 ` bugzilla-daemon

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