On 22/10/2019 13:23, Nicolas Saenz Julienne wrote: > 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; I'd try to avoid the goto. Apart from that we should write some information message that the crashkernel got reserved in arm64_dma_phys_limit. Otherwise RPi4 might break silently and this will give the user at least a hint what happened. Regards, Matthias > + } 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 >
