On riscv, the current crash kernel allocation logic is trying to allocate within 32bit addressible memory region by default, if failed, try to allocate without 4G restriction. In need of saving DMA zone memory while allocating a relatively large crash kernel region, allocating the reserved memory top down in high memory, without overlapping the DMA zone, is a mature solution. Hence this patchset introduces the parameter option crashkernel=X,[high,low]. One can reserve the crash kernel from high memory above DMA zone range by explicitly passing "crashkernel=X,high"; or reserve a memory range below 4G with "crashkernel=X,low". Besides, there are few rules need to take notice: 1. "crashkernel=X,[high,low]" will be ignored if "crashkernel=size" is specified. 2. "crashkernel=X,low" is valid only when "crashkernel=X,high" is passed and there is enough memory to be allocated under 4G. 3. When allocating crashkernel above 4G and no "crashkernel=X,low" is specified, a 128M low memory will be allocated automatically for swiotlb bounce buffer. See Documentation/admin-guide/kernel-parameters.txt for more information. To verify loading the crashkernel, adapted kexec-tools is attached below: https://github.com/chenjh005/kexec-tools/tree/build-test-riscv-v2 Following test cases have been performed as expected: 1) crashkernel=256M //low=256M 2) crashkernel=1G //low=1G 3) crashkernel=4G //high=4G, low=128M(default) 4) crashkernel=4G crashkernel=256M,high //high=4G, low=128M(default), high is ignored 5) crashkernel=4G crashkernel=256M,low //high=4G, low=128M(default), low is ignored 6) crashkernel=4G,high //high=4G, low=128M(default) 7) crashkernel=256M,low //low=0M, invalid 8) crashkernel=4G,high crashkernel=256M,low //high=4G, low=256M 9) crashkernel=4G,high crashkernel=4G,low //high=0M, low=0M, invalid 10) crashkernel=512M@0xd0000000 //low=512M 11) crashkernel=1G,high crashkernel=0M,low //high=1G, low=0M Changes since [v9]: 1. As per Conor's comment, rebase to correct base on riscv/for-next branch. No code logic changed. Changes since [v8]: 1. Rebase to newest mainline head, not modifying any code logic. Changes since [v7]: 1. Minor refactor: move crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE into the !high branch when the first allocation fails. Not changing the result but further align with Arm64 logic, refer to Baoquan's comment. 2. Add test case "crashkernel=1G,high crashkernel=0M,low", the result also matches our expectation. Changes since [v6]: 1. Introduce the "high" flag to mark whether "crashkernel=X,high" is passed. Fix the retrying logic between "crashkernel=X,high" case and others when the first allocation attempt fails. Changes since [v5]: 1. Update the crashkernel allocation logic when crashkernel=X,high is specified. In this case, region above 4G will directly get reserved as crashkernel, rather than trying lower 32bit allocation first. Changes since [v4]: 1. Update some imprecise code comments for cmdline parsing. Changes since [v3]: 1. Update to print warning and return explicitly on failure when crashkernel=size@offset is specified. Not changing the result in this case but making the logic more straightforward. 2. Some minor cleanup. Changes since [v2]: 1. Update the allocation logic to ensure the high crashkernel region is reserved strictly above dma32_phys_limit. 2. Clean up some minor format problems. Chen Jiahao (2): riscv: kdump: Implement crashkernel=X,[high,low] docs: kdump: Update the crashkernel description for riscv .../admin-guide/kernel-parameters.txt | 15 +-- arch/riscv/kernel/setup.c | 5 + arch/riscv/mm/init.c | 93 +++++++++++++++++-- 3 files changed, 99 insertions(+), 14 deletions(-) -- 2.34.1
