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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jul 05, 2022 at 06:05:01PM +0100, Catalin Marinas wrote: > On Tue, Jul 05, 2022 at 06:57:53PM +0300, Mike Rapoport wrote: > > On Tue, Jul 05, 2022 at 04:34:09PM +0100, Catalin Marinas wrote: > > > On Tue, Jul 05, 2022 at 06:02:02PM +0300, Mike Rapoport wrote: > > > > +void __init remap_crashkernel(void) > > > > +{ > > > > +#ifdef CONFIG_KEXEC_CORE > > > > + phys_addr_t start, end, size; > > > > + phys_addr_t aligned_start, aligned_end; > > > > + > > > > + if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) > > > > + return; > > > > + > > > > + if (!crashk_res.end) > > > > + return; > > > > + > > > > + start = crashk_res.start & PAGE_MASK; > > > > + end = PAGE_ALIGN(crashk_res.end); > > > > + > > > > + aligned_start = ALIGN_DOWN(crashk_res.start, PUD_SIZE); > > > > + aligned_end = ALIGN(end, PUD_SIZE); > > > > + > > > > + /* Clear PUDs containing crash kernel memory */ > > > > + unmap_hotplug_range(__phys_to_virt(aligned_start), > > > > + __phys_to_virt(aligned_end), false, NULL); > > > > > > What I don't understand is what happens if there's valid kernel data > > > between aligned_start and crashk_res.start (or the other end of the > > > range). > > > > Data shouldn't go anywhere :) > > > > There is > > > > + /* map area from PUD start to start of crash kernel with large pages */ > > + size = start - aligned_start; > > + __create_pgd_mapping(swapper_pg_dir, aligned_start, > > + __phys_to_virt(aligned_start), > > + size, PAGE_KERNEL, early_pgtable_alloc, 0); > > > > and > > > > + /* map area from end of crash kernel to PUD end with large pages */ > > + size = aligned_end - end; > > + __create_pgd_mapping(swapper_pg_dir, end, __phys_to_virt(end), > > + size, PAGE_KERNEL, early_pgtable_alloc, 0); > > > > after the unmap, so after we tear down a part of a linear map we > > immediately recreate it, just with a different page size. > > > > This all happens before SMP, so there is no concurrency at that point. > > That brief period of unmap worries me. The kernel text, data and stack > are all in the vmalloc space but any other (memblock) allocation to this > point may be in the unmapped range before and after the crashkernel > reservation. The interrupts are off, so I think the only allocation and > potential access that may go in this range is the page table itself. But > it looks fragile to me. I agree there are chances there will be an allocation from the unmapped range. We can make sure this won't happen, though. We can cap the memblock allocations with memblock_set_current_limit(aligned_end) or memblock_reserve(algined_start, aligned_end) until the mappings are restored. > -- > Catalin -- Sincerely yours, Mike. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel