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Tue, 20 May 2025 08:30:24 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id mUMCFKA9LGjgSgAAD6G6ig (envelope-from ); Tue, 20 May 2025 08:30:24 +0000 Date: Tue, 20 May 2025 10:30:18 +0200 From: Oscar Salvador To: Mike Rapoport Cc: Andrew Morton , Alexandre Ghiti , Pratyush Yadav , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm/cma: make detection of highmem_start more robust Message-ID: References: <20250519171805.1288393-1-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250519171805.1288393-1-rppt@kernel.org> X-Rspamd-Action: no action X-Stat-Signature: ubjrzo4wbc4i8rqtsskytbik5d187nuk X-Rspam-User: X-Rspamd-Queue-Id: 3BC02100014 X-Rspamd-Server: rspam06 X-HE-Tag: 1747729827-329519 X-HE-Meta: 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 f1A== 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 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. -- Oscar Salvador SUSE Labs