Messages in this thread | | | Subject | Re: [PATCH v4 1/5] arm64: export memblock_reserve()d regions via /proc/iomem | From | James Morse <> | Date | Tue, 21 Aug 2018 17:48:05 +0100 |
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On 08/21/2018 11:22 AM, James Morse wrote: > On 08/21/2018 05:39 AM, John Stultz wrote: >> On Sun, Jul 22, 2018 at 6:57 PM, AKASHI Takahiro >> <takahiro.akashi@linaro.org> wrote: >>> From: James Morse <james.morse@arm.com> >>> >>> There has been some confusion around what is necessary to prevent kexec >>> overwriting important memory regions. memblock: reserve, or nomap? >>> Only memblock nomap regions are reported via /proc/iomem, kexec's >>> user-space doesn't know about memblock_reserve()d regions. >>> >>> Until commit f56ab9a5b73ca ("efi/arm: Don't mark ACPI reclaim memory >>> as MEMBLOCK_NOMAP") the ACPI tables were nomap, now they are reserved >>> and thus possible for kexec to overwrite with the new kernel or initrd. >>> But this was always broken, as the UEFI memory map is also reserved >>> and not marked as nomap. >>> >>> Exporting both nomap and reserved memblock types is a nuisance as >>> they live in different memblock structures which we can't walk at >>> the same time. >>> >>> Take a second walk over memblock.reserved and add new 'reserved' >>> subnodes for the memblock_reserved() regions that aren't already >>> described by the existing code. (e.g. Kernel Code) >>> >>> We use reserve_region_with_split() to find the gaps in existing named >>> regions. This handles the gap between 'kernel code' and 'kernel data' >>> which is memblock_reserve()d, but already partially described by >>> request_standard_resources(). e.g.: >>> | 80000000-dfffffff : System RAM >>> | 80080000-80ffffff : Kernel code >>> | 81000000-8158ffff : reserved >>> | 81590000-8237efff : Kernel data >>> | a0000000-dfffffff : Crash kernel >>> | e00f0000-f949ffff : System RAM >>> >>> reserve_region_with_split needs kzalloc() which isn't available when >>> request_standard_resources() is called, use an initcall. > >>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c >>> index 30ad2f085d1f..5b4fac434c84 100644 >>> --- a/arch/arm64/kernel/setup.c >>> +++ b/arch/arm64/kernel/setup.c >>> @@ -241,6 +241,44 @@ static void __init request_standard_resources(void) > >>> +static int __init reserve_memblock_reserved_regions(void) > >>> + for_each_reserved_mem_region(i, &start, &end) { >>> + if (end <= roundup_end) >>> + continue; /* done already */ >>> + >>> + start = __pfn_to_phys(PFN_DOWN(start)); >>> + end = __pfn_to_phys(PFN_UP(end)) - 1; >>> + roundup_end = end; >>> + >>> + res = kzalloc(sizeof(*res), GFP_ATOMIC); >>> + if (WARN_ON(!res)) >>> + return -ENOMEM; >>> + res->start = start; >>> + res->end = end; >>> + res->name = "reserved"; >>> + res->flags = IORESOURCE_MEM; >>> + >>> + mem = request_resource_conflict(&iomem_resource, res); >>> + /* >>> + * We expected memblock_reserve() regions to conflict with >>> + * memory created by request_standard_resources(). >>> + */ >>> + if (WARN_ON_ONCE(!mem))
>> Since this patch landed, on the HiKey board at bootup I'm seeing: >> >> [ 0.451884] WARNING: CPU: 1 PID: 1 at arch/arm64/kernel/setup.c:271 >> reserve_memblock_reserved_regions+0xd4/0x13c
>> From skimming the patch, it seems this is maybe expected? Or should >> this warning raise eyebrows? I can't quite figure it out. > > Ugh, sorry for the noise! This is warning that there is something wrong > with our assumptions about what types of memory exist. > > >> It seems to trigger on the pstore memory at 0x21f00000-0x21ffffff. > > ... pmem ...
> So, this is a memblock_reserved() range that isn't actually memory. > > This happens because your DT has carved these regions out of the memory > node, but added a named 'reserved-memory' region for them, just in case? > I'm not sure what it means if 'reserved-memory' is not also described as > memory.... > > You do need the carve-out, otherwise this gets covered by the linear > map, and when you throw in that 'unbuffered' property you get both a > cacheable and uncacheable mapping of the same page.
Hmm, looks like its (even) more complicated than I thought, of_reserved_mem.c's definition of 'nomap' is memblock_remove(), not memblock_mark_nomap().
This might be more common to all users of DTs memreserve.
Thanks,
James
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