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[2003:cb:c70b:5f00:9b61:28a2:eea1:fa49]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4282b8adc7dsm26951425e9.14.2024.07.31.09.33.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Jul 2024 09:33:54 -0700 (PDT) Message-ID: <2b0131cf-d066-44ba-96d9-a611448cbaf9@redhat.com> Date: Wed, 31 Jul 2024 18:33:52 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/hugetlb: fix hugetlb vs. core-mm PT locking To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, James Houghton , stable@vger.kernel.org, Oscar Salvador , Muchun Song , Baolin Wang , Michael Ellerman , Christophe Leroy , Nicholas Piggin References: <20240731122103.382509-1-david@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 31.07.24 16:54, Peter Xu wrote: > On Wed, Jul 31, 2024 at 02:21:03PM +0200, David Hildenbrand wrote: >> We recently made GUP's common page table walking code to also walk hugetlb >> VMAs without most hugetlb special-casing, preparing for the future of >> having less hugetlb-specific page table walking code in the codebase. >> Turns out that we missed one page table locking detail: page table locking >> for hugetlb folios that are not mapped using a single PMD/PUD. >> >> Assume we have hugetlb folio that spans multiple PTEs (e.g., 64 KiB >> hugetlb folios on arm64 with 4 KiB base page size). GUP, as it walks the >> page tables, will perform a pte_offset_map_lock() to grab the PTE table >> lock. >> >> However, hugetlb that concurrently modifies these page tables would >> actually grab the mm->page_table_lock: with USE_SPLIT_PTE_PTLOCKS, the >> locks would differ. Something similar can happen right now with hugetlb >> folios that span multiple PMDs when USE_SPLIT_PMD_PTLOCKS. >> >> This issue can be reproduced [1], for example triggering: >> >> [ 3105.936100] ------------[ cut here ]------------ >> [ 3105.939323] WARNING: CPU: 31 PID: 2732 at mm/gup.c:142 try_grab_folio+0x11c/0x188 >> [ 3105.944634] Modules linked in: [...] >> [ 3105.974841] CPU: 31 PID: 2732 Comm: reproducer Not tainted 6.10.0-64.eln141.aarch64 #1 >> [ 3105.980406] Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20240524-4.fc40 05/24/2024 >> [ 3105.986185] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) >> [ 3105.991108] pc : try_grab_folio+0x11c/0x188 >> [ 3105.994013] lr : follow_page_pte+0xd8/0x430 >> [ 3105.996986] sp : ffff80008eafb8f0 >> [ 3105.999346] x29: ffff80008eafb900 x28: ffffffe8d481f380 x27: 00f80001207cff43 >> [ 3106.004414] x26: 0000000000000001 x25: 0000000000000000 x24: ffff80008eafba48 >> [ 3106.009520] x23: 0000ffff9372f000 x22: ffff7a54459e2000 x21: ffff7a546c1aa978 >> [ 3106.014529] x20: ffffffe8d481f3c0 x19: 0000000000610041 x18: 0000000000000001 >> [ 3106.019506] x17: 0000000000000001 x16: ffffffffffffffff x15: 0000000000000000 >> [ 3106.024494] x14: ffffb85477fdfe08 x13: 0000ffff9372ffff x12: 0000000000000000 >> [ 3106.029469] x11: 1fffef4a88a96be1 x10: ffff7a54454b5f0c x9 : ffffb854771b12f0 >> [ 3106.034324] x8 : 0008000000000000 x7 : ffff7a546c1aa980 x6 : 0008000000000080 >> [ 3106.038902] x5 : 00000000001207cf x4 : 0000ffff9372f000 x3 : ffffffe8d481f000 >> [ 3106.043420] x2 : 0000000000610041 x1 : 0000000000000001 x0 : 0000000000000000 >> [ 3106.047957] Call trace: >> [ 3106.049522] try_grab_folio+0x11c/0x188 >> [ 3106.051996] follow_pmd_mask.constprop.0.isra.0+0x150/0x2e0 >> [ 3106.055527] follow_page_mask+0x1a0/0x2b8 >> [ 3106.058118] __get_user_pages+0xf0/0x348 >> [ 3106.060647] faultin_page_range+0xb0/0x360 >> [ 3106.063651] do_madvise+0x340/0x598 >> >> Let's make huge_pte_lockptr() effectively use the same PT locks as any >> core-mm page table walker would. Add ptep_lockptr() to obtain the PTE >> page table lock using a pte pointer -- unfortunately we cannot convert >> pte_lockptr() because virt_to_page() doesn't work with kmap'ed page >> tables we can have with CONFIG_HIGHPTE. >> >> Take care of PTE tables possibly spanning multiple pages, and take care of >> CONFIG_PGTABLE_LEVELS complexity when e.g., PMD_SIZE == PUD_SIZE. For >> example, with CONFIG_PGTABLE_LEVELS == 2, core-mm would detect >> with hugepagesize==PMD_SIZE pmd_leaf() and use the pmd_lockptr(), which >> would end up just mapping to the per-MM PT lock. >> >> There is one ugly case: powerpc 8xx, whereby we have an 8 MiB hugetlb >> folio being mapped using two PTE page tables. While hugetlb wants to take >> the PMD table lock, core-mm would grab the PTE table lock of one of both >> PTE page tables. In such corner cases, we have to make sure that both >> locks match, which is (fortunately!) currently guaranteed for 8xx as it >> does not support SMP and consequently doesn't use split PT locks. >> >> [1] https://lore.kernel.org/all/1bbfcc7f-f222-45a5-ac44-c5a1381c596d@redhat.com/ >> >> Fixes: 9cb28da54643 ("mm/gup: handle hugetlb in the generic follow_page_mask code") >> Reviewed-by: James Houghton >> Cc: >> Cc: Peter Xu >> Cc: Oscar Salvador >> Cc: Muchun Song >> Cc: Baolin Wang >> Signed-off-by: David Hildenbrand > > Nitpick: I wonder whether some of the lines can be simplified if we write > it downwards from PUD, like, > > huge_pte_lockptr() > { > if (size >= PUD_SIZE) > return pud_lockptr(...); > if (size >= PMD_SIZE) > return pmd_lockptr(...); > /* Sub-PMD only applies to !CONFIG_HIGHPTE, see pte_alloc_huge() */ > WARN_ON(IS_ENABLED(CONFIG_HIGHPTE)); > return ptep_lockptr(...); > } Let me think about it. For PUD_SIZE == PMD_SIZE instead of like core-mm calling pmd_lockptr we'd call pud_lockptr(). Likely it would work because we default in most cases to the per-MM lock: arch/x86/Kconfig: select ARCH_ENABLE_SPLIT_PMD_PTLOCK if (PGTABLE_LEVELS > 2) && (X86_64 || X86_PAE) > > The ">=" checks should avoid checking over pgtable level, iiuc. > > The other nitpick is, I didn't yet find any arch that use non-zero order > page for pte pgtables. I would give it a shot with dropping the mask thing > then see what explodes (which I don't expect any, per my read..), but yeah > I understand we saw some already due to other things, so I think it's fine > in this hugetlb path (that we're removing) we do a few more math if you > think that's easier for you. I threw BUILD_BUG_ON(PTRS_PER_PTE * sizeof(pte_t) > PAGE_SIZE); into pte_lockptr() and did a bunch of cross-compiles. And for some reason it blows up for powernv (powernv_defconfig) and pseries (pseries_defconfig). In function 'pte_lockptr', inlined from 'pte_offset_map_nolock' at mm/pgtable-generic.c:316:11: ././include/linux/compiler_types.h:510:45: error: call to '__compiletime_assert_291' declared with attribute error: BUILD_BUG_ON failed: PTRS_PER_PTE * sizeof(pte_t) > PAGE_SIZE 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^ ././include/linux/compiler_types.h:491:25: note: in definition of macro '__compiletime_assert' 491 | prefix ## suffix(); \ | ^~~~~~ ././include/linux/compiler_types.h:510:9: note: in expansion of macro '_compiletime_assert' 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^~~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG' 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) | ^~~~~~~~~~~~~~~~ ./include/linux/mm.h:2926:9: note: in expansion of macro 'BUILD_BUG_ON' 2926 | BUILD_BUG_ON(PTRS_PER_PTE * sizeof(pte_t) > PAGE_SIZE); | ^~~~~~~~~~~~ In function 'pte_lockptr', inlined from '__pte_offset_map_lock' at mm/pgtable-generic.c:374:8: ././include/linux/compiler_types.h:510:45: error: call to '__compiletime_assert_291' declared with attribute error: BUILD_BUG_ON failed: PTRS_PER_PTE * sizeof(pte_t) > PAGE_SIZE 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^ ././include/linux/compiler_types.h:491:25: note: in definition of macro '__compiletime_assert' 491 | prefix ## suffix(); \ | ^~~~~~ ././include/linux/compiler_types.h:510:9: note: in expansion of macro '_compiletime_assert' 510 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^~~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG' 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) | ^~~~~~~~~~~~~~~~ ./include/linux/mm.h:2926:9: note: in expansion of macro 'BUILD_BUG_ON' 2926 | BUILD_BUG_ON(PTRS_PER_PTE * sizeof(pte_t) > PAGE_SIZE); | ^~~~~~~~~~~~ pte_alloc_one() ends up calling pte_fragment_alloc(mm, 0). But there we always end up calling pagetable_alloc(, 0). And fragments are supposed to be <= a single page. Now I'm confused what's wrong here ... am I missing something obvious? CCing some powerpc folks. Is this some pte_t oddity? But in mm_inc_nr_ptes/mm_dec_nr_ptes we use the exact same calculation :/ -- Cheers, David / dhildenb