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[2003:cb:c700:7e00:c672:608:5b3e:df8c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42caeb8b7f1sm143705455e9.48.2024.09.11.06.14.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Sep 2024 06:14:30 -0700 (PDT) Message-ID: <1e722a8f-0d07-40d0-aa30-4ee43dff7951@redhat.com> Date: Wed, 11 Sep 2024 15:14:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] mm: Abstract THP allocation To: Dev Jain , akpm@linux-foundation.org, willy@infradead.org, kirill.shutemov@linux.intel.com Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, mark.rutland@arm.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, jglisse@google.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240911065600.1002644-1-dev.jain@arm.com> <20240911065600.1002644-2-dev.jain@arm.com> <8bc0e51b-0e9b-4eeb-997f-e2a0b1a0c0f8@arm.com> <62df853c-98fb-4900-9cc6-04208e9611c6@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11.09.24 15:05, Dev Jain wrote: > > On 9/11/24 18:30, David Hildenbrand wrote: >> On 11.09.24 14:53, Dev Jain wrote: >>> >>> On 9/11/24 14:57, David Hildenbrand wrote: >>>> On 11.09.24 08:55, Dev Jain wrote: >>>>> In preparation for the second patch, abstract away the THP allocation >>>>> logic present in the create_huge_pmd() path, which corresponds to the >>>>> faulting case when no page is present. >>>>> >>>>> There should be no functional change as a result of applying >>>>> this patch. >>>>> >>>> >>>> [...] >>>> >>>>> + >>>>> +static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf, >>>>> +            struct vm_area_struct *vma, unsigned long haddr) >>>>> +{ >>>>> +    pmd_t entry; >>>>> + >>>>> +    entry = mk_huge_pmd(&folio->page, vma->vm_page_prot); >>>>> +    entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); >>>>> +    folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE); >>>>> +    folio_add_lru_vma(folio, vma); >>>>> +    set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry); >>>>> +    update_mmu_cache_pmd(vma, vmf->address, vmf->pmd); >>>> >>>> It's quite weird to see a mixture of haddr and vmf->address, and >>>> likely this mixture is wrong or not not required. >>>> >>>> Looking at arc's update_mmu_cache_pmd() implementation, I cannot see >>>> how passing in the unaligned address would do the right thing. But >>>> maybe arc also doesn't trigger that code path ... who knows :) >>> >>> If I am reading correctly, arch/arc/mm/tlb.c: update_mmu_cache_pmd() >>> calls update_mmu_cache_range() which is already expecting an unaligned >>> address? But... >> >> So update_mmu_cache_pmd() calls >> >>     update_mmu_cache_range(NULL, vma, addr, &pte, HPAGE_PMD_NR); >> >> But update_mmu_cache_range() only aligns it *to page boundary*: >> >>     unsigned long vaddr = vaddr_unaligned & PAGE_MASK; > > Ah, totally missed that it was PAGE_MASK. Thanks. >> >> We obtain the correct hugepage-aligned physical address from the PTE >> >>     phys_addr_t paddr = pte_val(*ptep) & PAGE_MASK_PHYS; >> >> Then, we look at the offset in our folio >> >>     unsigned long offset = offset_in_folio(folio, paddr); >> >> And adjust both vaddr and paddr >> >>     paddr -= offset; >>     vaddr -= offset; >> >> To then use that combination with >> >>     __inv_icache_pages(paddr, vaddr, nr); >> >> If I am not wrong, getting a non-hugepage aligned vaddr messes up >> things here. But only regarding the icache I think. > > Looks like it... As we are adding a fresh page where there previously wasn't anything mapped (no icache invaldiation required?), and because most anon mappings are not executable, maybe that's why nobody notices so far. -- Cheers, David / dhildenb