On Mon, 2019-10-21 at 16:36 -0400, Qian Cai wrote: > I managed to get more information here, > > [ 0.000000] cma: dma_contiguous_reserve(limit c0000000) > [ 0.000000] cma: dma_contiguous_reserve: reserving 64 MiB for global area > [ 0.000000] cma: cma_declare_contiguous(size 0x0000000004000000, base > 0x0000000000000000, limit 0x00000000c0000000 alignment 0x0000000000000000) > [ 0.000000] cma: Failed to reserve 512 MiB > > Full dmesg: > > https://cailca.github.io/files/dmesg.txt OK I got it, reproduced it too. Here are the relevant logs: [ 0.000000] DMA [mem 0x00000000802f0000-0x00000000bfffffff] [ 0.000000] DMA32 [mem 0x00000000c0000000-0x00000000ffffffff] [ 0.000000] Normal [mem 0x0000000100000000-0x00000097fcffffff] As you can see ZONE_DMA spans from 0x00000000802f0000-0x00000000bfffffff which is slightly smaller than 1GB. [ 0.000000] crashkernel reserved: 0x000000009fe00000 - 0x00000000bfe00000 (512 MB) Here crashkernel reserved 512M in ZONE_DMA. [ 0.000000] cma: Failed to reserve 512 MiB CMA tried to allocate 512M in ZONE_DMA which fails as there is no enough space. Makes sense. A fix could be moving crashkernel reservations after CMA and then if unable to fit in ZONE_DMA try ZONE_DMA32 before bailing out. Maybe it's a little over the top, yet although most devices will be fine with ZONE_DMA32, the RPi4 needs crashkernel to be reserved in ZONE_DMA. My knowledge of Kdump is limited, so I'd love to see what Catalin has to say. Here's a tested patch of what I'm proposing: diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 120c26af916b..49f3c3a34ae2 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -76,6 +76,7 @@ phys_addr_t arm64_dma32_phys_limit __ro_after_init; static void __init reserve_crashkernel(void) { unsigned long long crash_base, crash_size; + phys_addr_t limit = arm64_dma_phys_limit; int ret; ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(), @@ -86,11 +87,14 @@ static void __init reserve_crashkernel(void) crash_size = PAGE_ALIGN(crash_size); +again: if (crash_base == 0) { /* Current arm64 boot protocol requires 2MB alignment */ - crash_base = memblock_find_in_range(0, ARCH_LOW_ADDRESS_LIMIT, - crash_size, SZ_2M); - if (crash_base == 0) { + crash_base = memblock_find_in_range(0, limit, crash_size, SZ_2M); + if (!crash_base && limit == arm64_dma_phys_limit) { + limit = arm64_dma32_phys_limit; + goto again; + } else if (!crash_base && limit == arm64_dma32_phys_limit) { pr_warn("cannot allocate crashkernel (size:0x%llx)\n", crash_size); return; @@ -448,13 +452,13 @@ void __init arm64_memblock_init(void) else arm64_dma32_phys_limit = PHYS_MASK + 1; - reserve_crashkernel(); - reserve_elfcorehdr(); high_memory = __va(memblock_end_of_DRAM() - 1) + 1; dma_contiguous_reserve(arm64_dma_phys_limit ? : arm64_dma32_phys_limit); + + reserve_crashkernel(); } void __init bootmem_init(void) Regards, Nicolas
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