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[2003:cb:c749:9100:c078:eec6:f2f4:dd3b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43118305c6bsm39740645e9.22.2024.10.11.04.40.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Oct 2024 04:40:35 -0700 (PDT) Message-ID: Date: Fri, 11 Oct 2024 13:40:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] mm: don't install PMD mappings when THPs are disabled by the hw/process/vma To: Ryan Roberts , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, kvm@vger.kernel.org, Andrew Morton , Hugh Dickins , Thomas Huth , "Matthew Wilcox (Oracle)" , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Kefeng Wang , Leo Fu References: <20241011102445.934409-1-david@redhat.com> <20241011102445.934409-3-david@redhat.com> <4fd20101-d15c-4f9b-93c1-c780734a2294@arm.com> From: David Hildenbrand 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: <4fd20101-d15c-4f9b-93c1-c780734a2294@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A006540015 X-Stat-Signature: scr3y84477szoo89n6jyzs36c9xd79pk X-Rspam-User: X-HE-Tag: 1728646836-226098 X-HE-Meta: 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 K8veGErZ 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 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 11.10.24 13:36, Ryan Roberts wrote: > On 11/10/2024 12:33, David Hildenbrand wrote: >> On 11.10.24 13:29, Ryan Roberts wrote: >>> On 11/10/2024 11:24, David Hildenbrand wrote: >>>> We (or rather, readahead logic :) ) might be allocating a THP in the >>>> pagecache and then try mapping it into a process that explicitly disabled >>>> THP: we might end up installing PMD mappings. >>>> >>>> This is a problem for s390x KVM, which explicitly remaps all PMD-mapped >>>> THPs to be PTE-mapped in s390_enable_sie()->thp_split_mm(), before >>>> starting the VM. >>>> >>>> For example, starting a VM backed on a file system with large folios >>>> supported makes the VM crash when the VM tries accessing such a mapping >>>> using KVM. >>>> >>>> Is it also a problem when the HW disabled THP using >>>> TRANSPARENT_HUGEPAGE_UNSUPPORTED? At least on x86 this would be the case >>>> without X86_FEATURE_PSE. >>>> >>>> In the future, we might be able to do better on s390x and only disallow >>>> PMD mappings -- what s390x and likely TRANSPARENT_HUGEPAGE_UNSUPPORTED >>>> really wants. For now, fix it by essentially performing the same check as >>>> would be done in __thp_vma_allowable_orders() or in shmem code, where this >>>> works as expected, and disallow PMD mappings, making us fallback to PTE >>>> mappings. >>>> >>>> Reported-by: Leo Fu >>>> Fixes: 793917d997df ("mm/readahead: Add large folio readahead") >>> >>> Will this patch be difficult to backport given it depends on the previous patch >>> and that doesn't have a Fixes tag? >> >> "difficult" -- not really. Andrew might want to tag patch #1  with "Fixes:" as >> well, but I can also send simple stable backports that avoid patch #1. >> >> (Thinking again, I assume we want to Cc:stable) >> >>> >>>> Cc: Thomas Huth >>>> Cc: Matthew Wilcox (Oracle) >>>> Cc: Ryan Roberts >>>> Cc: Christian Borntraeger >>>> Cc: Janosch Frank >>>> Cc: Claudio Imbrenda >>>> Signed-off-by: David Hildenbrand >>>> --- >>>>   mm/memory.c | 9 +++++++++ >>>>   1 file changed, 9 insertions(+) >>>> >>>> diff --git a/mm/memory.c b/mm/memory.c >>>> index 2366578015ad..a2e501489517 100644 >>>> --- a/mm/memory.c >>>> +++ b/mm/memory.c >>>> @@ -4925,6 +4925,15 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct >>>> page *page) >>>>       pmd_t entry; >>>>       vm_fault_t ret = VM_FAULT_FALLBACK; >>>>   +    /* >>>> +     * It is too late to allocate a small folio, we already have a large >>>> +     * folio in the pagecache: especially s390 KVM cannot tolerate any >>>> +     * PMD mappings, but PTE-mapped THP are fine. So let's simply refuse any >>>> +     * PMD mappings if THPs are disabled. >>>> +     */ >>>> +    if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags)) >>>> +        return ret; >>> >>> Why not just call thp_vma_allowable_orders()? >> >> Why call thp_vma_allowable_orders() that does a lot more work that doesn't >> really apply here? :) > > Yeah fair enough, I was just thinking it makes the code simpler to keep all the > checks in one place. But no strong opinion. > > Either way: > > Reviewed-by: Ryan Roberts Thanks! Also, I decided to not use "thp_vma_allowable_orders" because we are past the allocation phase (as indicated in the comment) and can really just change the way how we map the folio (PMD vs. PTE), not really *what* folio to use. Ideally, in the future we have a different way of just saying "no PMD mappings please", decoupling the mapping from the allocation granularity. -- Cheers, David / dhildenb