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[2003:cb:c70b:e100:38d6:8aa1:11b0:a20a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-385ccd36b80sm18477515f8f.29.2024.12.04.08.00.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Dec 2024 08:00:55 -0800 (PST) Message-ID: Date: Wed, 4 Dec 2024 17:00:53 +0100 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: [GIT PULL] arm64 updates for 6.13-rc1 To: Catalin Marinas Cc: Yang Shi , Sasha Levin , Linus Torvalds , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20241118100623.2674026-1-catalin.marinas@arm.com> <0c09425b-c8ba-4ed6-b429-0bce4e7d00e9@os.amperecomputing.com> <6aec1d44-4a89-4acf-a16b-4493626b93bb@os.amperecomputing.com> <4919faec-3e35-459f-a7d3-b5b3f188bd9c@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: 8bit On 04.12.24 16:50, Catalin Marinas wrote: > On Wed, Dec 04, 2024 at 04:32:11PM +0100, David Hildenbrand wrote: >> On 04.12.24 16:29, Catalin Marinas wrote: >>> On Mon, Dec 02, 2024 at 08:22:57AM -0800, Yang Shi wrote: >>>> On 11/28/24 1:56 AM, David Hildenbrand wrote: >>>>> On 28.11.24 02:21, Yang Shi wrote: >>>>>>>> diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c >>>>>>>> index 87b3f1a25535..ef303a2262c5 100644 >>>>>>>> --- a/arch/arm64/mm/copypage.c >>>>>>>> +++ b/arch/arm64/mm/copypage.c >>>>>>>> @@ -30,9 +30,9 @@ void copy_highpage(struct page *to, struct >>>>>>>> page *from) >>>>>>>>         if (!system_supports_mte()) >>>>>>>>             return; >>>>>>>> -    if (folio_test_hugetlb(src) && >>>>>>>> -        folio_test_hugetlb_mte_tagged(src)) { >>>>>>>> -        if (!folio_try_hugetlb_mte_tagging(dst)) >>>>>>>> +    if (folio_test_hugetlb(src)) { >>>>>>>> +        if (!folio_test_hugetlb_mte_tagged(src) || >>>>>>>> +            !folio_try_hugetlb_mte_tagging(dst)) >>>>>>>>                 return; >>>>>>>>             /* >>>>>>> I wonder why we had a 'return' here originally rather than a >>>>>>> WARN_ON_ONCE() as we do further down for the page case. Do you seen any >>>>>>> issue with the hunk below? Destination should be a new folio and not >>>>>>> tagged yet: >>>>>> >>>>>> Yes, I did see problem. Because we copy tags for all sub pages then set >>>>>> folio mte tagged when copying the data for the first subpage. The >>>>>> warning will be triggered when we copy the second subpage. >>>>> >>>>> It's rather weird, though. We're instructed to copy a single page, yet >>>>> copy tags for all pages. >>>>> >>>>> This really only makes sense when called from folio_copy(), where we are >>>>> guaranteed to copy all pages. >>>>> >>>>> I'm starting to wonder if we should be able to hook into / overload >>>>> folio_copy() instead, to just handle the complete hugetlb copy ourselves >>>>> in one shot, and assume that copy_highpage() will never be called for >>>>> hugetlb pages (WARN and don't copy tags). >>>> >>>> Actually folio_copy() is just called by migration. Copy huge page in CoW is >>>> more complicated and uses copy_user_highpage()->copy_highpage() instead of >>>> folio_copy(). It may start the page copy from any subpage. For example, if >>>> the CoW is triggered by accessing to the address in the middle of 2M. Kernel >>>> may copy the second half first then the first half to guarantee the accessed >>>> data in cache. >>> >>> Still trying to understand the possible call paths here. If we get a >>> write fault on a large folio, does the core code allocate a folio of the >>> same size for CoW or it starts with smaller ones? wp_page_copy() >>> allocates order 0 AFAICT, though if it was a pmd fault, it takes a >>> different path in handle_mm_fault(). But we also have huge pages using >>> contiguous ptes. >>> >>> Unless the source and destinations folios are exactly the same size, it >>> will break many assumptions in the code above. Going the other way >>> around is also wrong, dst larger than src, we are not initialising the >>> whole dst folio. >>> >>> Maybe going back to per-page PG_mte_tagged flag rather than per-folio >>> would keep things simple, less risk of wrong assumptions. >> >> I think the magic bit here is that for hugetlb, we only get hugetlb folios >> of the same size, and no mixtures. > > Ah, ok, we do check for this and only do the advance copy for hugetlb > folios. I'd add a check for folio size just in case, something like > below (I'll add some description and post it properly): > > diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c > index 87b3f1a25535..c3a83db46ec6 100644 > --- a/arch/arm64/mm/copypage.c > +++ b/arch/arm64/mm/copypage.c > @@ -30,11 +30,14 @@ void copy_highpage(struct page *to, struct page *from) > if (!system_supports_mte()) > return; > > - if (folio_test_hugetlb(src) && > - folio_test_hugetlb_mte_tagged(src)) { > - if (!folio_try_hugetlb_mte_tagging(dst)) > + if (folio_test_hugetlb(src)) { To be safe, maybe also test that dst is a hugetlb folio? But maybe the implicit checks we added in folio_try_hugetlb_mte_tagging() will already check that. > + if (!folio_test_hugetlb_mte_tagged(src) || > + from != folio_page(src, 0) || > + WARN_ON_ONCE(folio_nr_pages(src) != folio_nr_pages(dst))) > return; > > + WARN_ON_ONCE(!folio_try_hugetlb_mte_tagging(dst)); > + > /* > * Populate tags for all subpages. > * > -- Cheers, David / dhildenb