On Wed, Dec 13, 2017 at 10:49:27AM +0000, Ard Biesheuvel wrote: > On 13 December 2017 at 10:26, AKASHI Takahiro > <takahiro.akashi@xxxxxxxxxx> wrote: > > Bhupesh, Ard, > > > > On Wed, Dec 13, 2017 at 03:21:59AM +0530, Bhupesh Sharma wrote: > >> Hi Ard, Akashi > >> > > (snip) > > > >> Looking deeper into the issue, since the arm64 kexec-tools uses the > >> 'linux,usable-memory-range' dt property to allow crash dump kernel to > >> identify its own usable memory and exclude, at its boot time, any > >> other memory areas that are part of the panicked kernel's memory. > >> (see https://www.kernel.org/doc/Documentation/devicetree/bindings/chosen.txt > >> , for details) > > > > Right. > > > >> 1). Now when 'kexec -p' is executed, this node is patched up only > >> with the crashkernel memory range: > >> > >> /* add linux,usable-memory-range */ > >> nodeoffset = fdt_path_offset(new_buf, "/chosen"); > >> result = fdt_setprop_range(new_buf, nodeoffset, > >> PROP_USABLE_MEM_RANGE, &crash_reserved_mem, > >> address_cells, size_cells); > >> > >> (see https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/tree/kexec/arch/arm64/kexec-arm64.c#n465 > >> , for details) > >> > >> 2). This excludes the ACPI reclaim regions irrespective of whether > >> they are marked as System RAM or as RESERVED. As, > >> 'linux,usable-memory-range' dt node is patched up only with > >> 'crash_reserved_mem' and not 'system_memory_ranges' > >> > >> 3). As a result when the crashkernel boots up it doesn't find this > >> ACPI memory and crashes while trying to access the same: > >> > >> # kexec -p /boot/vmlinuz-`uname -r` --initrd=/boot/initramfs-`uname > >> -r`.img --reuse-cmdline -d > >> > >> [snip..] > >> > >> Reserved memory range > >> 000000000e800000-000000002e7fffff (0) > >> > >> Coredump memory ranges > >> 0000000000000000-000000000e7fffff (0) > >> 000000002e800000-000000003961ffff (0) > >> 0000000039d40000-000000003ed2ffff (0) > >> 000000003ed60000-000000003fbfffff (0) > >> 0000001040000000-0000001ffbffffff (0) > >> 0000002000000000-0000002ffbffffff (0) > >> 0000009000000000-0000009ffbffffff (0) > >> 000000a000000000-000000affbffffff (0) > >> > >> 4). So if we revert Ard's patch or just comment the fixing up of the > >> memory cap'ing passed to the crash kernel inside > >> 'arch/arm64/mm/init.c' (see below): > >> > >> static void __init fdt_enforce_memory_region(void) > >> { > >> struct memblock_region reg = { > >> .size = 0, > >> }; > >> > >> of_scan_flat_dt(early_init_dt_scan_usablemem, ®); > >> > >> if (reg.size) > >> //memblock_cap_memory_range(reg.base, reg.size); /* > >> comment this out */ > >> } > > > > Please just don't do that. It can cause a fatal damage on > > memory contents of the *crashed* kernel. > > > >> 5). Both the above temporary solutions fix the problem. > >> > >> 6). However exposing all System RAM regions to the crashkernel is not > >> advisable and may cause the crashkernel or some crashkernel drivers to > >> fail. > >> > >> 6a). I am trying an approach now, where the ACPI reclaim regions are > >> added to '/proc/iomem' separately as ACPI reclaim regions by the > >> kernel code and on the other hand the user-space 'kexec-tools' will > >> pick up the ACPI reclaim regions from '/proc/iomem' and add it to the > >> dt node 'linux,usable-memory-range' > > > > I still don't understand why we need to carry over the information > > about "ACPI Reclaim memory" to crash dump kernel. In my understandings, > > such regions are free to be reused by the kernel after some point of > > initialization. Why does crash dump kernel need to know about them? > > > > Not really. According to the UEFI spec, they can be reclaimed after > the OS has initialized, i.e., when it has consumed the ACPI tables and > no longer needs them. Of course, in order to be able to boot a kexec > kernel, those regions needs to be preserved, which is why they are > memblock_reserve()'d now. For my better understandings, who is actually accessing such regions during boot time, uefi itself or efistub? > So it seems that kexec does not honour the memblock_reserve() table > when booting the next kernel. not really. > > (In other words, can or should we skip some part of ACPI-related init code > > on crash dump kernel?) > > > > I don't think so. And the change to the handling of ACPI reclaim > regions only revealed the bug, not created it (given that other > memblock_reserve regions may be affected as well) As whether we should honor such reserved regions over kexec'ing depends on each one's specific nature, we will have to take care one-by-one. As a matter of fact, no information about "reserved" memblocks is exposed to user space (via proc/iomem). -Takahiro AKASHI > > >> 6b). The kernel code currently looks like the following: > >> > >> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c > >> index 30ad2f085d1f..867bdec7c692 100644 > >> --- a/arch/arm64/kernel/setup.c > >> +++ b/arch/arm64/kernel/setup.c > >> @@ -206,6 +206,7 @@ static void __init request_standard_resources(void) > >> { > >> struct memblock_region *region; > >> struct resource *res; > >> + phys_addr_t addr_start, addr_end; > >> > >> kernel_code.start = __pa_symbol(_text); > >> kernel_code.end = __pa_symbol(__init_begin - 1); > >> @@ -218,9 +219,17 @@ static void __init request_standard_resources(void) > >> res->name = "reserved"; > >> res->flags = IORESOURCE_MEM; > >> } else { > >> - res->name = "System RAM"; > >> - res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY; > >> + addr_start = > >> __pfn_to_phys(memblock_region_reserved_base_pfn(region)); > >> + addr_end = > >> __pfn_to_phys(memblock_region_reserved_end_pfn(region)) - 1; > >> + if ((efi_mem_type(addr_start) == EFI_ACPI_RECLAIM_MEMORY) > >> || (efi_mem_type(addr_end) == EFI_ACPI_RECLAIM_MEMORY)) { > >> + res->name = "ACPI reclaim region"; > >> + res->flags = IORESOURCE_MEM; > >> + } else { > >> + res->name = "System RAM"; > >> + res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY; > >> + } > >> } > >> + > >> res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region)); > >> res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 1; > >> > >> @@ -292,6 +301,7 @@ void __init setup_arch(char **cmdline_p) > >> > >> request_standard_resources(); > >> > >> + efi_memmap_unmap(); > >> early_ioremap_reset(); > >> > >> if (acpi_disabled) > >> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c > >> index 80d1a885def5..a7c522eac640 100644 > >> --- a/drivers/firmware/efi/arm-init.c > >> +++ b/drivers/firmware/efi/arm-init.c > >> @@ -259,7 +259,6 @@ void __init efi_init(void) > >> > >> reserve_regions(); > >> efi_esrt_init(); > >> - efi_memmap_unmap(); > >> > >> memblock_reserve(params.mmap & PAGE_MASK, > >> PAGE_ALIGN(params.mmap_size + > >> > >> > >> After this change the ACPI reclaim regions are properly recognized in > >> '/proc/iomem': > >> > >> # cat /proc/iomem | grep -i ACPI > >> 396c0000-3975ffff : ACPI reclaim region > >> 39770000-397affff : ACPI reclaim region > >> 398a0000-398bffff : ACPI reclaim region > >> > >> 6c). I am currently changing the 'kexec-tools' and will finish the > >> testing over the next few days. > >> > >> I just wanted to know your opinion on this issue, so that I will be > >> able to propose a fix on the above lines. > >> > >> Also Cc'ing kexec mailing list for more inputs on changes proposed to > >> kexec-tools. > >> > >> Thanks, > >> Bhupesh -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
