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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431bd8e8549sm190894735e9.10.2024.11.04.07.42.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Nov 2024 07:42:03 -0800 (PST) Message-ID: <0f306d3d-38e3-4ce3-a161-7695ea9392cd@redhat.com> Date: Mon, 4 Nov 2024 16:42:01 +0100 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 6.6.y] mm: don't install PMD mappings when THPs are disabled by the hw/process/vma To: stable@vger.kernel.org Cc: Leo Fu , Thomas Huth , "Matthew Wilcox (Oracle)" , Ryan Roberts , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Hugh Dickins , Kefeng Wang , Greg KH References: <2024101842-empty-espresso-c8a3@gregkh> <20241022090952.4101444-1-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: <20241022090952.4101444-1-david@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Gentle ping, XEN PV users reported an issue fixed by this fix upstream. On 22.10.24 11:09, 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. > > Link: https://lkml.kernel.org/r/20241011102445.934409-3-david@redhat.com > Fixes: 793917d997df ("mm/readahead: Add large folio readahead") > Signed-off-by: David Hildenbrand > Reported-by: Leo Fu > Tested-by: Thomas Huth > Cc: Thomas Huth > Cc: Matthew Wilcox (Oracle) > Cc: Ryan Roberts > Cc: Christian Borntraeger > Cc: Janosch Frank > Cc: Claudio Imbrenda > Cc: Hugh Dickins > Cc: Kefeng Wang > Cc: > Signed-off-by: Andrew Morton > (cherry picked from commit 2b0f922323ccfa76219bcaacd35cd50aeaa13592) > Signed-off-by: David Hildenbrand > --- > > Minor contextual difference. > > Note that the backport of 963756aac1f011d904ddd9548ae82286d3a91f96 is > required (send separately as reply to the "FAILED:" mail). > > --- > mm/memory.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index b6ddfe22c5d5..742c2f65c2c8 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4293,6 +4293,15 @@ 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; > + > if (!transhuge_vma_suitable(vma, haddr)) > return ret; > -- Cheers, David / dhildenb