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b=Gr9+9juMaC4yBKHu3TlC785iHTeskDfBKwt4tl5GFw6pNheVAt5mcGODyKL39f1Vw iu48ERRPf3g7ynMKx3u+/TGGgaEy6YyezXlLYRgwEGJEgN45WV0QJrYT/lGl8/PzQ3 3dJC/Y7N9tFkDZrST/LHgaiZhqc2Bbpf2wxeiEWmPY0dtvQC4CtMaWhFZTa9o7HJEB SPKAd/CdofoKcwC9mj+iQMuW/pTkGi3crrRQB/ojfC5pkXO69obg4pgHQCWQ/+Q/wn YO4+m+4QwH24386w+ez2g5LgUw18MdjXEDRJ3YcqxxjAd4cBycPpbOaRBK0z97dA2T PW7s4xGb8VSUw== Message-ID: <105963ed-b489-4b82-973a-9024d74c6e87@kernel.org> Date: Mon, 29 Jan 2024 13:43:39 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/debug_vm_pgtable: Fix BUG_ON with pud advanced test Content-Language: en-US To: Anshuman Khandual , linux-mm@kvack.org, akpm@linux-foundation.org Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org References: <20240129060022.68044-1-aneesh.kumar@kernel.org> <1b3c1513-826d-4908-93c3-212a6f1b2d74@arm.com> <504f70be-deca-4f7f-b28c-d1ec2cf5a348@kernel.org> From: "Aneesh Kumar K.V" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: CDEEB4000E X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: yxkgjykrte7tercm4ud98p3w8usyhdg7 X-HE-Tag: 1706516028-690360 X-HE-Meta: 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 GISzDmDx HzqyePr0yEMhlE+qGovrB1lKus+I3u4BMM/DmMQji5ZL/Q4YKNgGbY8bDSrL1vQC71vEIjUOS8GTdf2aY0NeDBmiFGbJAhrCT0y4t2DmttfYJBTLkU2n+fSdpkA5grJcURv+GFRiXqYj08EWNR9ir4pyb3Z1an4qOA0aTNyG/+qEGZBZlWLcED/kq8+rNJmOOyo3d9VEUjZSkHoEdxvF/GMOVYx5kBPpKmm2vTidXN288akZ48fiUI5rTkwQICczUTwkzJoaCfdTUS1vPnZw42F4re45cYCbuhFLaVUmNUvzmy2AZaFEE3AvurQJk7DqhgUAEUNvWfoZQ1iI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/29/24 12:23 PM, Anshuman Khandual wrote: > > > On 1/29/24 11:56, Aneesh Kumar K.V wrote: >> On 1/29/24 11:52 AM, Anshuman Khandual wrote: >>> >>> >>> On 1/29/24 11:30, Aneesh Kumar K.V (IBM) wrote: >>>> Architectures like powerpc add debug checks to ensure we find only devmap >>>> PUD pte entries. These debug checks are only done with CONFIG_DEBUG_VM. >>>> This patch marks the ptes used for PUD advanced test devmap pte entries >>>> so that we don't hit on debug checks on architecture like ppc64 as >>>> below. >>>> >>>> WARNING: CPU: 2 PID: 1 at arch/powerpc/mm/book3s64/radix_pgtable.c:1382 radix__pud_hugepage_update+0x38/0x138 >>>> .... >>>> NIP [c0000000000a7004] radix__pud_hugepage_update+0x38/0x138 >>>> LR [c0000000000a77a8] radix__pudp_huge_get_and_clear+0x28/0x60 >>>> Call Trace: >>>> [c000000004a2f950] [c000000004a2f9a0] 0xc000000004a2f9a0 (unreliable) >>>> [c000000004a2f980] [000d34c100000000] 0xd34c100000000 >>>> [c000000004a2f9a0] [c00000000206ba98] pud_advanced_tests+0x118/0x334 >>>> [c000000004a2fa40] [c00000000206db34] debug_vm_pgtable+0xcbc/0x1c48 >>>> [c000000004a2fc10] [c00000000000fd28] do_one_initcall+0x60/0x388 >>>> >>>> Also >>>> >>>> kernel BUG at arch/powerpc/mm/book3s64/pgtable.c:202! >>>> .... >>>> >>>> NIP [c000000000096510] pudp_huge_get_and_clear_full+0x98/0x174 >>>> LR [c00000000206bb34] pud_advanced_tests+0x1b4/0x334 >>>> Call Trace: >>>> [c000000004a2f950] [000d34c100000000] 0xd34c100000000 (unreliable) >>>> [c000000004a2f9a0] [c00000000206bb34] pud_advanced_tests+0x1b4/0x334 >>>> [c000000004a2fa40] [c00000000206db34] debug_vm_pgtable+0xcbc/0x1c48 >>>> [c000000004a2fc10] [c00000000000fd28] do_one_initcall+0x60/0x388 >>>> >>>> Fixes: 27af67f35631 ("powerpc/book3s64/mm: enable transparent pud hugepage") >>>> Signed-off-by: Aneesh Kumar K.V (IBM) >>>> --- >>>> mm/debug_vm_pgtable.c | 8 ++++++++ >>>> 1 file changed, 8 insertions(+) >>>> >>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c >>>> index 5662e29fe253..65c19025da3d 100644 >>>> --- a/mm/debug_vm_pgtable.c >>>> +++ b/mm/debug_vm_pgtable.c >>>> @@ -362,6 +362,12 @@ static void __init pud_advanced_tests(struct pgtable_debug_args *args) >>>> vaddr &= HPAGE_PUD_MASK; >>>> >>>> pud = pfn_pud(args->pud_pfn, args->page_prot); >>>> + /* >>>> + * Some architectures have debug checks to make sure >>>> + * huge pud mapping are only found with devmap entries >>>> + * For now test with only devmap entries. >>>> + */ >>> Do you see this behaviour to be changed in powerpc anytime soon ? Otherwise >>> these pud_mkdevmap() based work arounds, might be required to stick around >>> for longer just to prevent powerpc specific triggers. Given PUD transparent >>> huge pages i.e HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD are just supported on x86 >>> and powerpc platforms, could not this problem be solved in a more uniform >>> manner. >>> >> >> >> IIUC pud level transparent hugepages are only supported with devmap entries even >> on x86. We don't do anonymous pud hugepage. > > There are some 'pud_trans_huge(orig_pud) || pud_devmap(orig_pud)' checks in > core paths i.e in mm/memory.c which might suggest pud_trans_huge() to exist > without also being a devmap. I might be missing something here, but on x86 > platform following helpers suggest pud_trans_huge() to exist without being > a devmap as well. > > #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD > static inline int pud_trans_huge(pud_t pud) > { > return (pud_val(pud) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE; > } > #endif > > #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD > static inline int pud_devmap(pud_t pud) > { > return !!(pud_val(pud) & _PAGE_DEVMAP); > } > #else > static inline int pud_devmap(pud_t pud) > { > return 0; > } > #endif > > We might need some more clarity on this regarding x86 platform's pud huge > page implementation. > static vm_fault_t create_huge_pud(struct vm_fault *vmf) { #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \ defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) struct vm_area_struct *vma = vmf->vma; /* No support for anonymous transparent PUD pages yet */ if (vma_is_anonymous(vma)) return VM_FAULT_FALLBACK; if (vma->vm_ops->huge_fault) return vma->vm_ops->huge_fault(vmf, PUD_ORDER); #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ return VM_FAULT_FALLBACK; } -aneesh