Hi James, On 2019/6/6 0:29, James Morse wrote: > Hello, > > On 07/05/2019 04:50, Chen Zhou wrote: >> When crashkernel is reserved above 4G in memory, kernel should >> reserve some amount of low memory for swiotlb and some DMA buffers. > >> Meanwhile, support crashkernel=X,[high,low] in arm64. When use >> crashkernel=X parameter, try low memory first and fall back to high >> memory unless "crashkernel=X,high" is specified. > > What is the 'unless crashkernel=...,high' for? I think it would be simpler to relax the > ARCH_LOW_ADDRESS_LIMIT if reserve_crashkernel_low() allocated something. > > This way "crashkernel=1G" tries to allocate 1G below 4G, but fails if there isn't enough > memory. "crashkernel=1G crashkernel=16M,low" allocates 16M below 4G, which is more likely > to succeed, if it does it can then place the 1G block anywhere. > Yeah, this is much simpler. > >> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c >> index 413d566..82cd9a0 100644 >> --- a/arch/arm64/kernel/setup.c >> +++ b/arch/arm64/kernel/setup.c >> @@ -243,6 +243,9 @@ static void __init request_standard_resources(void) >> request_resource(res, &kernel_data); >> #ifdef CONFIG_KEXEC_CORE >> /* Userspace will find "Crash kernel" region in /proc/iomem. */ >> + if (crashk_low_res.end && crashk_low_res.start >= res->start && >> + crashk_low_res.end <= res->end) >> + request_resource(res, &crashk_low_res); >> if (crashk_res.end && crashk_res.start >= res->start && >> crashk_res.end <= res->end) >> request_resource(res, &crashk_res); > > With both crashk_low_res and crashk_res, we end up with two entries in /proc/iomem called > "Crash kernel". Because its sorted by address, and kexec-tools stops searching when it > find "Crash kernel", you are always going to get the kernel placed in the lower portion. > > I suspect this isn't what you want, can we rename crashk_low_res for arm64 so that > existing kexec-tools doesn't use it? > In my patchset, in addition to the kernel patches, i also modify the kexec-tools. arm64: support more than one crash kernel regions(http://lists.infradead.org/pipermail/kexec/2019-April/022792.html). In kexec-tools patch, we read all the "Crash kernel" entry and load crash kernel high. > >> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >> index d2adffb..3fcd739 100644 >> --- a/arch/arm64/mm/init.c >> +++ b/arch/arm64/mm/init.c >> @@ -74,20 +74,37 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init; >> static void __init reserve_crashkernel(void) >> { >> unsigned long long crash_base, crash_size; >> + bool high = false; >> int ret; >> >> ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(), >> &crash_size, &crash_base); >> /* no crashkernel= or invalid value specified */ >> - if (ret || !crash_size) >> - return; >> + if (ret || !crash_size) { >> + /* crashkernel=X,high */ >> + ret = parse_crashkernel_high(boot_command_line, >> + memblock_phys_mem_size(), >> + &crash_size, &crash_base); >> + if (ret || !crash_size) >> + return; >> + high = true; >> + } >> >> crash_size = PAGE_ALIGN(crash_size); >> >> 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); >> + /* >> + * Try low memory first and fall back to high memory >> + * unless "crashkernel=size[KMG],high" is specified. >> + */ >> + if (!high) >> + crash_base = memblock_find_in_range(0, >> + ARCH_LOW_ADDRESS_LIMIT, >> + crash_size, CRASH_ALIGN); >> + if (!crash_base) >> + crash_base = memblock_find_in_range(0, >> + memblock_end_of_DRAM(), >> + crash_size, CRASH_ALIGN); >> if (crash_base == 0) { >> pr_warn("cannot allocate crashkernel (size:0x%llx)\n", >> crash_size); >> @@ -105,13 +122,18 @@ static void __init reserve_crashkernel(void) >> return; >> } >> >> - if (!IS_ALIGNED(crash_base, SZ_2M)) { >> + if (!IS_ALIGNED(crash_base, CRASH_ALIGN)) { >> pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n"); >> return; >> } >> } >> memblock_reserve(crash_base, crash_size); >> >> + if (crash_base >= SZ_4G && reserve_crashkernel_low()) { >> + memblock_free(crash_base, crash_size); >> + return; > > This is going to be annoying on platforms that don't have, and don't need memory below 4G. > A "crashkernel=...,low" on these system will break crashdump. I don't think we should > expect users to know the memory layout. (I'm assuming distro's are going to add a low > reservation everywhere, just in case) > > I think the 'low' region should be a small optional/best-effort extra, that kexec-tools > can't touch. > > > I'm afraid you've missed the ugly bit of the crashkernel reservation... > > arch/arm64/mm/mmu.c::map_mem() marks the crashkernel as 'nomap' during the first pass of > page-table generation. This means it isn't mapped in the linear map. It then maps it with > page-size mappings, and removes the nomap flag. > > This is done so that arch_kexec_protect_crashkres() and > arch_kexec_unprotect_crashkres() can remove the valid bits of the crashkernel mapping. > This way the old-kernel can't accidentally overwrite the crashkernel. It also saves us if > the old-kernel and the crashkernel use different memory attributes for the mapping. > > As your low-memory reservation is intended to be used for devices, having it mapped by the > old-kernel as cacheable memory is going to cause problems if those CPUs aren't taken > offline and go corrupting this memory. (we did crash for a reason after all) > > > I think the simplest thing to do is mark the low region as 'nomap' in > reserve_crashkernel() and always leave it unmapped. We can then describe it via a > different string in /proc/iomem, something like "Crash kernel (low)". Older kexec-tools > shouldn't use it, (I assume its not using strncmp() in a way that would do this by > accident), and newer kexec-tools can know to describe it in the DT, but it can't write to it. > I did miss the bit of the crashkernel reservation. I will fix this in next version. > > Thanks, > > James > > . > Thanks, Chen Zhou
