Bhupesh, Can you test the patch attached below, please? It is intended to retain already-reserved regions (ACPI reclaim memory in this case) in system ram (i.e. memblock.memory) without explicitly exporting them via usable-memory-range. (I still have to figure out what the side-effect of this patch is.) Thanks, -Takahiro AKASHI On Thu, Dec 21, 2017 at 01:30:43AM +0530, Bhupesh Sharma wrote: > On Tue, Dec 19, 2017 at 6:39 PM, Ard Biesheuvel > <ard.biesheuvel at linaro.org> wrote: > > On 19 December 2017 at 07:09, AKASHI Takahiro > > <takahiro.akashi at linaro.org> wrote: > >> On Mon, Dec 18, 2017 at 01:40:09PM +0800, Dave Young wrote: > >>> On 12/15/17 at 05:59pm, AKASHI Takahiro wrote: > >>> > On Wed, Dec 13, 2017 at 12:17:22PM +0000, Ard Biesheuvel wrote: > >>> > > On 13 December 2017 at 12:16, AKASHI Takahiro > >>> > > <takahiro.akashi at linaro.org> wrote: > >>> > > > On Wed, Dec 13, 2017 at 10:49:27AM +0000, Ard Biesheuvel wrote: > >>> > > >> On 13 December 2017 at 10:26, AKASHI Takahiro > >>> > > >> <takahiro.akashi at linaro.org> 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? > >>> > > > > >>> > > > >>> > > No, only the kernel. This is where the ACPI tables are stored. For > >>> > > instance, on QEMU we have > >>> > > > >>> > > ACPI: RSDP 0x0000000078980000 000024 (v02 BOCHS ) > >>> > > ACPI: XSDT 0x0000000078970000 000054 (v01 BOCHS BXPCFACP 00000001 > >>> > > 01000013) > >>> > > ACPI: FACP 0x0000000078930000 00010C (v05 BOCHS BXPCFACP 00000001 > >>> > > BXPC 00000001) > >>> > > ACPI: DSDT 0x0000000078940000 0011DA (v02 BOCHS BXPCDSDT 00000001 > >>> > > BXPC 00000001) > >>> > > ACPI: APIC 0x0000000078920000 000140 (v03 BOCHS BXPCAPIC 00000001 > >>> > > BXPC 00000001) > >>> > > ACPI: GTDT 0x0000000078910000 000060 (v02 BOCHS BXPCGTDT 00000001 > >>> > > BXPC 00000001) > >>> > > ACPI: MCFG 0x0000000078900000 00003C (v01 BOCHS BXPCMCFG 00000001 > >>> > > BXPC 00000001) > >>> > > ACPI: SPCR 0x00000000788F0000 000050 (v02 BOCHS BXPCSPCR 00000001 > >>> > > BXPC 00000001) > >>> > > ACPI: IORT 0x00000000788E0000 00007C (v00 BOCHS BXPCIORT 00000001 > >>> > > BXPC 00000001) > >>> > > > >>> > > covered by > >>> > > > >>> > > efi: 0x0000788e0000-0x00007894ffff [ACPI Reclaim Memory ...] > >>> > > ... > >>> > > efi: 0x000078970000-0x00007898ffff [ACPI Reclaim Memory ...] > >>> > > >>> > OK. I mistakenly understood those regions could be freed after exiting > >>> > UEFI boot services. > >>> > > >>> > > > >>> > > >> 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). > >>> > > > > >>> > > > >>> > > That is why I suggested (somewhere in this thread?) to not expose them > >>> > > as 'System RAM'. Do you think that could solve this? > >>> > > >>> > Memblock-reserv'ing them is necessary to prevent their corruption and > >>> > marking them under another name in /proc/iomem would also be good in order > >>> > not to allocate them as part of crash kernel's memory. > >>> > > >>> > But I'm not still convinced that we should export them in useable- > >>> > memory-range to crash dump kernel. They will be accessed through > >>> > acpi_os_map_memory() and so won't be required to be part of system ram > >>> > (or memblocks), I guess. > >>> > -> Bhupesh? > >>> > >>> I forgot how arm64 kernel retrieve the memory ranges and initialize > >>> them. If no "e820" like interfaces shouldn't kernel reinitialize all > >>> the memory according to the efi memmap? For kdump kernel anything other > >>> than usable memory (which is from the dt node instead) should be > >>> reinitialized according to efi passed info, no? > >> > >> All the regions exported in efi memmap will be added to memblock.memory > >> in (u)efi_init() and then trimmed down to the exact range specified as > >> usable-memory-range by fdt_enforce_memory_region(). > >> > >> Now I noticed that the current fdt_enforce_memory_region() may not work well > >> with multiple entries in usable-memory-range. > >> > > > > In any case, the root of the problem is that memory regions lose their > > 'memory' annotation due to the way the memory map is mangled before > > being supplied to the kexec kernel. > > > > Would it be possible to classify all memory that we want to hide from > > the kexec kernel as NOMAP instead? That way, it will not be mapped > > implicitly, but will still be mapped cacheable by acpi_os_ioremap(), > > so this seems to be the most appropriate way to deal with the host > > kernel's memory contents. > > Hmm. wouldn't appending the acpi reclaim regions to > 'linux,usable-memory-range' in the dtb being passed to the crashkernel > be better? Because its indirectly achieving a similar objective > (although may be a subset of all System RAM regions on the primary > kernel's memory). > > I am not aware of the background about the current kexec-tools > implementation where we add only the crashkernel range to the dtb > being passed to the crashkernel. > > Probably Akashi can answer better, as to how we arrived at this design > approach and why we didn't want to expose all System RAM regions (i.e. > ! NOMPAP regions) to the crashkernel. > > I am suspecting that some issues were seen/meet when the System RAM (! > NOMAP regions) were exposed to the crashkernel, and that's why we > finalized on this design approach, but this is something which is just > my guess. > > Regards, > Bhupesh > > >>> > > >>> > Just FYI, on x86, ACPI tables seems to be exposed to crash dump kernel > >>> > via a kernel command line parameter, "memmap=". > >>> > >>> memmap= is only used in old kexec-tools, now we are passing them via > >>> e820 table. > >> > >> Thanks. I remember that you have explained it before. > >> > >> -Takahiro AKASHI > >> > >>> [snip] > >>> > >>> Thanks > >>> Dave ===8<== >From 74e2451fea83d546feae76160ba7de426913fe03 Mon Sep 17 00:00:00 2001 From: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> Date: Thu, 21 Dec 2017 19:14:23 +0900 Subject: [PATCH] arm64: kdump: mark unusable memory as NOMAP --- arch/arm64/mm/init.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 00e7b900ca41..8175db94257b 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -352,11 +352,17 @@ static void __init fdt_enforce_memory_region(void) struct memblock_region reg = { .size = 0, }; + u64 idx; + phys_addr_t start, end; of_scan_flat_dt(early_init_dt_scan_usablemem, ®); - if (reg.size) - memblock_cap_memory_range(reg.base, reg.size); + if (reg.size) { + for_each_free_mem_range(idx, NUMA_NO_NODE, MEMBLOCK_NONE, + &start, &end, NULL) + memblock_mark_nomap(start, end - start); + memblock_clear_nomap(reg.base, reg.size); + } } void __init arm64_memblock_init(void) -- 2.15.1
