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[91.12.110.127]) by smtp.gmail.com with ESMTPSA id dn1-20020a0560000c0100b0033ec7182673sm1481745wrb.52.2024.03.22.01.13.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Mar 2024 01:13:03 -0700 (PDT) Message-ID: <17c1f86e-e6bf-4be0-88cd-c4afecb02310@redhat.com> Date: Fri, 22 Mar 2024 09:13:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm/userfaultfd: don't place zeropages when zeropages are disallowed To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Andrew Morton , Alexander Gordeev , Sven Schnelle , Gerald Schaefer , Andrea Arcangeli , kvm@vger.kernel.org, linux-s390@vger.kernel.org References: <20240321215954.177730-1-david@redhat.com> <20240321215954.177730-2-david@redhat.com> <48d1282c-e4db-4b55-ab3f-3344af2440c4@redhat.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: 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: 7bit X-Stat-Signature: m8ypwk1nbg1d8iruff7368ahegzmnx7w X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 5A3F6140018 X-Rspam-User: X-HE-Tag: 1711095188-977093 X-HE-Meta: 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 5X3bWfsi jciqkvrou6ZJweAAIA16WGiSCmiPm2w/EDsfr8LonnK/69wRLES+RBCtOtrZSLO2oc668FnTrtgTvfR3oCgq30wtQFSgxnUhn0OOpss8rHbRLppOIjdgyOeJpimGtU3jQMMR/I/LmyzHd/JPF/3dsWOqVqWioGNDzA+HpSOqye8lZt+E= 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 21.03.24 23:46, Peter Xu wrote: > On Thu, Mar 21, 2024 at 11:29:45PM +0100, David Hildenbrand wrote: >> On 21.03.24 23:20, Peter Xu wrote: >>> On Thu, Mar 21, 2024 at 10:59:53PM +0100, David Hildenbrand wrote: >>>> s390x must disable shared zeropages for processes running VMs, because >>>> the VMs could end up making use of "storage keys" or protected >>>> virtualization, which are incompatible with shared zeropages. >>>> >>>> Yet, with userfaultfd it is possible to insert shared zeropages into >>>> such processes. Let's fallback to simply allocating a fresh zeroed >>>> anonymous folio and insert that instead. >>>> >>>> mm_forbids_zeropage() was introduced in commit 593befa6ab74 ("mm: introduce >>>> mm_forbids_zeropage function"), briefly before userfaultfd went >>>> upstream. >>>> >>>> Note that we don't want to fail the UFFDIO_ZEROPAGE request like we do >>>> for hugetlb, it would be rather unexpected. Further, we also >>>> cannot really indicated "not supported" to user space ahead of time: it >>>> could be that the MM disallows zeropages after userfaultfd was already >>>> registered. >>>> >>>> Fixes: c1a4de99fada ("userfaultfd: mcopy_atomic|mfill_zeropage: UFFDIO_COPY|UFFDIO_ZEROPAGE preparation") >>>> Signed-off-by: David Hildenbrand >>> >>> Reviewed-by: Peter Xu >>> >>> Still, a few comments below. >>> >>>> --- >>>> mm/userfaultfd.c | 35 +++++++++++++++++++++++++++++++++++ >>>> 1 file changed, 35 insertions(+) >>>> >>>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >>>> index 712160cd41eca..1d1061ccd1dea 100644 >>>> --- a/mm/userfaultfd.c >>>> +++ b/mm/userfaultfd.c >>>> @@ -316,6 +316,38 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd, >>>> goto out; >>>> } >>>> +static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd, >>>> + struct vm_area_struct *dst_vma, unsigned long dst_addr) >>>> +{ >>>> + struct folio *folio; >>>> + int ret; >>> >>> nitpick: we can set -ENOMEM here, then >>> >>>> + >>>> + folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr); >>>> + if (!folio) >>>> + return -ENOMEM; >>> >>> return ret; >>> >>>> + >>>> + ret = -ENOMEM; >>> >>> drop. >> >> Sure! >> >>> >>>> + if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) >>>> + goto out_put; >>>> + >>>> + /* >>>> + * The memory barrier inside __folio_mark_uptodate makes sure that >>>> + * preceding stores to the page contents become visible before >>>> + * the set_pte_at() write. >>>> + */ >>> >>> This comment doesn't apply. We can drop it. >>> >> >> I thought the same until I spotted that comment (where uffd originally >> copied this from I strongly assume) in do_anonymous_page(). >> >> "Preceding stores" here are: zeroing out the memory. > > Ah.. that's okay then. > > Considering that userfault used to be pretty cautious on such ordering, as > its specialty to involve many user updates on the page, would you mind we > mention those details out? > > /* > * __folio_mark_uptodate contains the memory barrier to make sure > * the page updates to the zero page will be visible before > * installing the pgtable entries. See do_anonymous_page(). > */ > > Or anything better than my wordings. Sure, I'd slightly reword it. The following on top: diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 1d1061ccd1dea..9d385696fb891 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -320,20 +320,19 @@ static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr) { struct folio *folio; - int ret; + int ret = -ENOMEM; folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr); if (!folio) - return -ENOMEM; + return ret; - ret = -ENOMEM; if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) goto out_put; /* * The memory barrier inside __folio_mark_uptodate makes sure that - * preceding stores to the page contents become visible before - * the set_pte_at() write. + * zeroing out the folio become visible before mapping the page + * using set_pte_at(). See do_anonymous_page(). */ __folio_mark_uptodate(folio); Thanks! -- Cheers, David / dhildenb