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(p200300cbc70a4d00b9689e7aaf8badf7.dip0.t-ipconnect.de. [2003:cb:c70a:4d00:b968:9e7a:af8b:adf7]) by smtp.gmail.com with ESMTPSA id g7-20020a5d5407000000b003392206c808sm9629533wrv.105.2024.02.13.06.05.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Feb 2024 06:05:15 -0800 (PST) Message-ID: Date: Tue, 13 Feb 2024 15:05:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 19/25] arm64/mm: Wire up PTE_CONT for user mappings To: Ryan Roberts , Ard Biesheuvel Cc: Mark Rutland , Catalin Marinas , Will Deacon , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240202080756.1453939-1-ryan.roberts@arm.com> <20240202080756.1453939-20-ryan.roberts@arm.com> <64395ae4-3a7d-45dd-8f1d-ea6b232829c5@arm.com> <41499621-482f-455b-9f68-b43ea8052557@redhat.com> <1d302d7a-50ab-4ab4-b049-75ed4a71a87d@arm.com> <99e2a92c-f2a2-4e1e-8ce2-08caae2cb7e4@redhat.com> <64b872bd-4b12-4dbd-b043-1ad11aeaa19a@redhat.com> <3de2130b-9f0f-4a11-ac06-7bf814de641c@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: <3de2130b-9f0f-4a11-ac06-7bf814de641c@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-Rspam-User: X-Stat-Signature: poc9j4zxqd8afa7t9tzd68ttsqstocj3 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4AD1F8001C X-HE-Tag: 1707833139-351308 X-HE-Meta: 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 7zHbcI5B IsGu24KmCl3CaHyimXIE+Up7ktGPlwD0jBAm/+pWAyHJr9qMrra3LHZ53pgX8aOphuWs+Xjt2XnO9l5x9k3uDtQC7lDr4OHb1cLwb4+FJH0Al6vIyN3D/rUaw04O+Nlz3lu9P/S2KflF8WrqcQAKh5ZMbwDr2nFRq+HuhxdZK507UdTORmoEV91YyL3+BnEZOr1KKphMnxcxjkuK0tRba75/6/F5HXC51CFZTBhEsLJ4iOA5pqCTJRxG2iKtQly+M1WzWQ1LwhDAX++mnyEIE9Bwz7mKo5QmoWjWif/Oiex/O7YuECyrm0lOQl3EIhbm9goXFWXLn5qyfIV+riuCaiUUzzHyTAsQFlkuv6/BkP98lrn9zhigDamYjNODHN2dk7YsNuyH4wCJ5XB9xKl04ymQ5Tr4RExJAa4JobqFWOVRjm7DMraqiN6wNWzK7+wT76Rf7DRTj9VNoV9MvRPCV3EWNvKXH+uESFBWZEEx41rVtt9tqXbGK3bYc4w6mzynUICZZzd3QBNdNR2i8jiQfzruO/rRINsf+gsgTDXRlyihu11FdBcXS1apTmbd83PsFI3EO6jLVuEXEcVGf8R1J0HimvnQSZQ4VrNq+vqTp/sQjBxnVZrEp2EiRqw== 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 13.02.24 15:02, Ryan Roberts wrote: > On 13/02/2024 13:45, David Hildenbrand wrote: >> On 13.02.24 14:33, Ard Biesheuvel wrote: >>> On Tue, 13 Feb 2024 at 14:21, Ryan Roberts wrote: >>>> >>>> On 13/02/2024 13:13, David Hildenbrand wrote: >>>>> On 13.02.24 14:06, Ryan Roberts wrote: >>>>>> On 13/02/2024 12:19, David Hildenbrand wrote: >>>>>>> On 13.02.24 13:06, Ryan Roberts wrote: >>>>>>>> On 12/02/2024 20:38, Ryan Roberts wrote: >>>>>>>>> [...] >>>>>>>>> >>>>>>>>>>>>> +static inline bool mm_is_user(struct mm_struct *mm) >>>>>>>>>>>>> +{ >>>>>>>>>>>>> +    /* >>>>>>>>>>>>> +     * Don't attempt to apply the contig bit to kernel mappings, >>>>>>>>>>>>> because >>>>>>>>>>>>> +     * dynamically adding/removing the contig bit can cause page >>>>>>>>>>>>> faults. >>>>>>>>>>>>> +     * These racing faults are ok for user space, since they get >>>>>>>>>>>>> serialized >>>>>>>>>>>>> +     * on the PTL. But kernel mappings can't tolerate faults. >>>>>>>>>>>>> +     */ >>>>>>>>>>>>> +    return mm != &init_mm; >>>>>>>>>>>>> +} >>>>>>>>>>>> >>>>>>>>>>>> We also have the efi_mm as a non-user mm, though I don't think we >>>>>>>>>>>> manipulate >>>>>>>>>>>> that while it is live, and I'm not sure if that needs any special >>>>>>>>>>>> handling. >>>>>>>>>>> >>>>>>>>>>> Well we never need this function in the hot (order-0 folio) path, so I >>>>>>>>>>> think I >>>>>>>>>>> could add a check for efi_mm here with performance implication. It's >>>>>>>>>>> probably >>>>>>>>>>> safest to explicitly exclude it? What do you think? >>>>>>>>>> >>>>>>>>>> Oops: This should have read "I think I could add a check for efi_mm here >>>>>>>>>> *without* performance implication" >>>>>>>>> >>>>>>>>> It turns out that efi_mm is only defined when CONFIG_EFI is enabled I >>>>>>>>> can do >>>>>>>>> this: >>>>>>>>> >>>>>>>>> return mm != &init_mm && (!IS_ENABLED(CONFIG_EFI) || mm != &efi_mm); >>>>>>>>> >>>>>>>>> Is that acceptable? This is my preference, but nothing else outside of efi >>>>>>>>> references this symbol currently. >>>>>>>>> >>>>>>>>> Or perhaps I can convince myself that its safe to treat efi_mm like >>>>>>>>> userspace. >>>>>>>>> There are a couple of things that need to be garanteed for it to be safe: >>>>>>>>> >>>>>>>>>      - The PFNs of present ptes either need to have an associated struct >>>>>>>>> page or >>>>>>>>>        need to have the PTE_SPECIAL bit set (either pte_mkspecial() or >>>>>>>>>        pte_mkdevmap()) >>>>>>>>> >>>>>>>>>      - Live mappings must either be static (no changes that could cause >>>>>>>>> fold/unfold >>>>>>>>>        while live) or the system must be able to tolerate a temporary fault >>>>>>>>> >>>>>>>>> Mark suggests efi_mm is not manipulated while live, so that meets the >>>>>>>>> latter >>>>>>>>> requirement, but I'm not sure about the former? >>>>>>>> >>>>>>>> I've gone through all the efi code, and conclude that, as Mark suggests, the >>>>>>>> mappings are indeed static. And additionally, the ptes are populated >>>>>>>> using only >>>>>>>> the _private_ ptep API, so there is no issue here. As just discussed with >>>>>>>> Mark, >>>>>>>> my prefereence is to not make any changes to code, and just add a comment >>>>>>>> describing why efi_mm is safe. >>>>>>>> >>>>>>>> Details: >>>>>>>> >>>>>>>> * Registered with ptdump >>>>>>>>        * ptep_get_lockless() >>>>>>>> * efi_create_mapping -> create_pgd_mapping … -> init_pte: >>>>>>>>        * __ptep_get() >>>>>>>>        * __set_pte() >>>>>>>> * efi_memattr_apply_permissions -> efi_set_mapping_permissions … -> >>>>>>>> set_permissions >>>>>>>>        * __ptep_get() >>>>>>>>        * __set_pte() >>>>>>> >>>>>>> Sound good. We could add some VM_WARN_ON if we ever get the efi_mm via the >>>>>>> "official" APIs. >>>>>> >>>>>> We could, but that would lead to the same linkage issue, which I'm trying to >>>>>> avoid in the first place: >>>>>> >>>>>> VM_WARN_ON(IS_ENABLED(CONFIG_EFI) && mm == efi_mm); >>>>>> >>>>>> This creates new source code dependencies, which I would rather avoid if >>>>>> possible. >>>>> >>>>> Just a thought, you could have a is_efi_mm() function that abstracts all that. >>>>> >>>>> diff --git a/include/linux/efi.h b/include/linux/efi.h >>>>> index c74f47711f0b..152f5fa66a2a 100644 >>>>> --- a/include/linux/efi.h >>>>> +++ b/include/linux/efi.h >>>>> @@ -692,6 +692,15 @@ extern struct efi { >>>>> >>>>>   extern struct mm_struct efi_mm; >>>>> >>>>> +static inline void is_efi_mm(struct mm_struct *mm) >>>>> +{ >>>>> +#ifdef CONFIG_EFI >>>>> +       return mm == &efi_mm; >>>>> +#else >>>>> +       return false; >>>>> +#endif >>>>> +} >>>>> + >>>>>   static inline int >>>>>   efi_guidcmp (efi_guid_t left, efi_guid_t right) >>>>>   { >>>>> >>>>> >>>> >>>> That would definitely work, but in that case, I might as well just check for it >>>> in mm_is_user() (and personally I would change the name to mm_is_efi()): >>>> >>>> >>>> static inline bool mm_is_user(struct mm_struct *mm) >>>> { >>>>          return mm != &init_mm && !mm_is_efi(mm); >>>> } >>>> >>>> Any objections? >>>> >>> >>> Any reason not to use IS_ENABLED(CONFIG_EFI) in the above? The extern >>> declaration is visible to the compiler, and any references should >>> disappear before the linker could notice that efi_mm does not exist. >>> >> >> Sure, as long as the linker is happy why not. I'll let Ryan mess with that :) > > I'm not sure if you are suggesting dropping the mm_is_efi() helper and just use > IS_ENABLED(CONFIG_EFI) in mm_is_user() to guard efi_mm, or if you are suggesting > using IS_ENABLED(CONFIG_EFI) in mm_is_efi() instead of the ifdefery? > > The former was what I did initially; It works great, but I didn't like that I > was introducing a new code dependecy between efi and arm64 (nothing else outside > of efi references efi_mm). > > So then concluded that it is safe to not worry about efi_mm (thanks for your > confirmation). But then David wanted a VM_WARN check, which reintroduces the > code dependency. So he suggested the mm_is_efi() helper to hide that... This is > all starting to feel circular... I think Ard meant that inside mm_is_efi(), we could avoid the #ifdef and simply use IS_ENABLED(). -- Cheers, David / dhildenb