Hi Tao, On Sat, Nov 25, 2023 at 09:51:54AM +0800, Tao Liu wrote: > Thanks for the idea of using CMA as part of memory for the 2nd kernel. > However I have a question: > > What if there is on-going DMA/RDMA access on the CMA range when 1st > kernel crash? There might be data corruption when 2nd kernel and > DMA/RDMA write to the same place, how to address such an issue? The crash kernel CMA area(s) registered via cma_declare_contiguous() are distinct from the dma_contiguous_default_area or device-specific CMA areas that dma_alloc_contiguous() would use to reserve memory for DMA. Kernel pages will not be allocated from the crash kernel CMA area(s), because they are not GFP_MOVABLE. The CMA area will only be used for user pages. User pages for RDMA, should be pinned with FOLL_LONGTERM and that would migrate them away from the CMA area. But you're right that DMA to user pages pinned without FOLL_LONGTERM would still be possible. Would this be a problem in practice? Do you see any way around it? Thanks, -- Jiri Bohac <jbohac@xxxxxxx> SUSE Labs, Prague, Czechia _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
