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[2003:d8:2f28:7c00:a95e:ac49:f2ad:ab84]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f73d4a3csm35883445e9.22.2025.05.20.08.08.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 May 2025 08:08:53 -0700 (PDT) Message-ID: Date: Tue, 20 May 2025 17:08:52 +0200 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: [PATCH] mm/cma: make detection of highmem_start more robust To: Mike Rapoport Cc: Oscar Salvador , Andrew Morton , Alexandre Ghiti , Pratyush Yadav , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250519171805.1288393-1-rppt@kernel.org> 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: 7bit On 20.05.25 17:06, Mike Rapoport wrote: > On Tue, May 20, 2025 at 11:14:28AM +0200, David Hildenbrand wrote: >> On 20.05.25 10:30, Oscar Salvador wrote: >>> On Mon, May 19, 2025 at 08:18:05PM +0300, Mike Rapoport wrote: >>>> From: "Mike Rapoport (Microsoft)" >>>> >>>> Pratyush Yadav reports the following crash: >>>> >>>> ------------[ cut here ]------------ >>>> kernel BUG at arch/x86/mm/physaddr.c:23! >>>> ception 0x06 IP 10:ffffffff812ebbf8 error 0 cr2 0xffff88903ffff000 >>>> CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.15.0-rc6+ #231 PREEMPT(undef) >>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014 >>>> RIP: 0010:__phys_addr+0x58/0x60 >>>> Code: 01 48 89 c2 48 d3 ea 48 85 d2 75 05 e9 91 52 cf 00 0f 0b 48 3d ff ff ff 1f 77 0f 48 8b 05 20 54 55 01 48 01 d0 e9 78 52 cf 00 <0f> 0b 90 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 >>>> RSP: 0000:ffffffff82803dd8 EFLAGS: 00010006 ORIG_RAX: 0000000000000000 >>>> RAX: 000000007fffffff RBX: 00000000ffffffff RCX: 0000000000000000 >>>> RDX: 000000007fffffff RSI: 0000000280000000 RDI: ffffffffffffffff >>>> RBP: ffffffff82803e68 R08: 0000000000000000 R09: 0000000000000000 >>>> R10: ffffffff83153180 R11: ffffffff82803e48 R12: ffffffff83c9aed0 >>>> R13: 0000000000000000 R14: 0000001040000000 R15: 0000000000000000 >>>> FS: 0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000 >>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>> CR2: ffff88903ffff000 CR3: 0000000002838000 CR4: 00000000000000b0 >>>> Call Trace: >>>> >>>> ? __cma_declare_contiguous_nid+0x6e/0x340 >>>> ? cma_declare_contiguous_nid+0x33/0x70 >>>> ? dma_contiguous_reserve_area+0x2f/0x70 >>>> ? setup_arch+0x6f1/0x870 >>>> ? start_kernel+0x52/0x4b0 >>>> ? x86_64_start_reservations+0x29/0x30 >>>> ? x86_64_start_kernel+0x7c/0x80 >>>> ? common_startup_64+0x13e/0x141 >>>> >>>> The reason is that __cma_declare_contiguous_nid() does: >>>> >>>> highmem_start = __pa(high_memory - 1) + 1; >>>> >>>> If dma_contiguous_reserve_area() (or any other CMA declaration) is >>>> called before free_area_init(), high_memory is uninitialized. Without >>>> CONFIG_DEBUG_VIRTUAL, it will likely work but use the wrong value for >>>> highmem_start. >>>> >>>> The issue occurs because commit e120d1bc12da ("arch, mm: set high_memory in >>>> free_area_init()") moved initialization of high_memory after the call to >>>> dma_contiguous_reserve() -> __cma_declare_contiguous_nid() on several >>>> architectures. >>>> >>>> In the case CONFIG_HIGHMEM is enabled, some architectures that actually >>>> support HIGHMEM (arm, powerpc and x86) have initialization of high_memory >>>> before a possible call to __cma_declare_contiguous_nid() and some >>>> initialized high_memory late anyway (arc, csky, microblase, mips, sparc, >>>> xtensa) even before the commit e120d1bc12da so they are fine with using >>>> uninitialized value of high_memory. >>>> >>>> And in the case CONFIG_HIGHMEM is disabled high_memory essentially becomes >>>> the first address after memory end, so instead of relying on high_memory to >>>> calculate highmem_start use memblock_end_of_DRAM() and eliminate the >>>> dependency of CMA area creation on high_memory in majority of >>>> configurations. >>>> >>>> Reported-by: Pratyush Yadav >>>> Tested-by: Alexandre Ghiti >>>> Signed-off-by: Mike Rapoport (Microsoft) >>> >>> Reviewed-by: Oscar Salvador >>> >>> I will note though that it is a bit akward to have highmem involved here >>> when we might not have CONFIG_HIGHMEM enabled. >>> I get that for !CONFIG_HIGHMEM it is a no-op situation, but still I >>> wonder whether we could abstract that from this function. > > Highmem is there for some time now (see f7426b983a6a ("mm: cma: adjust > address limit to avoid hitting low/high memory boundary")) > We might try abstracting it from that function but I'd prefer not doing it > that late in the release cycle. Agreed, assuming this will still make it into this release. > >> Same thought here. >> >> Can't we do some IS_ENABLED(CONFIG_HIGHMEM) magic or similar to not even use >> that variable without CONFIG_HIGHMEM? > > You mean highmem_start or high_memory? highmem_start in this function. > > high_memory is one of the ways to say "end of directly/linearly addressable > memory" and some other places in the kernel (outside arch) still use it > regardless of CONFIG_HIGHMEM. > > And I don't think we have another way to say where directly addressable > memory ends, and this IMHO is something that should replace high_memory. Agreed. -- Cheers, David / dhildenb