Messages in this thread | | | Subject | Re: [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory | From | David Hildenbrand <> | Date | Mon, 1 Feb 2021 15:32:33 +0100 |
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On 01.02.21 15:30, Mike Rapoport wrote: > On Mon, Feb 01, 2021 at 10:32:44AM +0100, David Hildenbrand wrote: >> On 30.01.21 23:10, Mike Rapoport wrote: >>> From: Mike Rapoport <rppt@linux.ibm.com> >>> >>> The physical memory on an x86 system starts at address 0, but this is not >>> always reflected in e820 map. For example, the BIOS can have e820 entries >>> like >>> >>> [ 0.000000] BIOS-provided physical RAM map: >>> [ 0.000000] BIOS-e820: [mem 0x0000000000001000-0x000000000009ffff] usable >>> >>> or >>> >>> [ 0.000000] BIOS-provided physical RAM map: >>> [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] reserved >>> [ 0.000000] BIOS-e820: [mem 0x0000000000001000-0x0000000000057fff] usable >>> >>> In either case, e820__memblock_setup() won't add the range 0x0000 - 0x1000 >>> to memblock.memory and later during memory map initialization this range is >>> left outside any zone. >>> >>> With SPARSEMEM=y there is always a struct page for pfn 0 and this struct >>> page will have it's zone link wrong no matter what value will be set there. >>> >>> To avoid this inconsistency, add the beginning of RAM to memblock.memory. >>> Limit the added chunk size to match the reserved memory to avoid >>> registering memory that may be used by the firmware but never reserved at >>> e820__memblock_setup() time. >>> >>> Fixes: bde9cfa3afe4 ("x86/setup: don't remove E820_TYPE_RAM for pfn 0") >>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> >>> Cc: stable@vger.kernel.org >>> --- >>> arch/x86/kernel/setup.c | 8 ++++++++ >>> 1 file changed, 8 insertions(+) >>> >>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c >>> index 3412c4595efd..67c77ed6eef8 100644 >>> --- a/arch/x86/kernel/setup.c >>> +++ b/arch/x86/kernel/setup.c >>> @@ -727,6 +727,14 @@ static void __init trim_low_memory_range(void) >>> * Kconfig help text for X86_RESERVE_LOW. >>> */ >>> memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE)); >>> + >>> + /* >>> + * Even if the firmware does not report the memory at address 0 as >>> + * usable, inform the generic memory management about its existence >>> + * to ensure it is a part of ZONE_DMA and the memory map for it is >>> + * properly initialized. >>> + */ >>> + memblock_add(0, ALIGN(reserve_low, PAGE_SIZE)); >>> } >>> >>> /* >>> >> >> I think, to make that code more robust, and to not rely on archs to do the >> right thing, we should do something like >> >> 1) Make sure in free_area_init() that each PFN with a memmap (i.e., falls >> into a partial present section) is spanned by a zone; that would include PFN >> 0 in this case. >> >> 2) In init_zone_unavailable_mem(), similar to round_up(max_pfn, >> PAGES_PER_SECTION) handling, consider range >> [round_down(min_pfn, PAGES_PER_SECTION), min_pfn - 1] >> which would handle in the x86-64 case [0..0] and, therefore, initialize PFN >> 0. >> >> Also, I think the special-case of PFN 0 is analogous to the >> round_up(max_pfn, PAGES_PER_SECTION) handling in >> init_zone_unavailable_mem(): who guarantees that these PFN above the highest >> present PFN are actually spanned by a zone? >> >> I'd suggest going through all zone ranges in free_area_init() first, dealing >> with zones that have "not section aligned start/end", clamping them up/down >> if required such that no holes within a section are left uncovered by a >> zone. > > I thought about changing the way zone extents are calculated so that zone > start/end will be always on a section boundary, but zone->zone_start_pfn > depends on node->node_start_pfn which is defined by hardware and expanding > a node to make its start pfn aligned at the section boundary might violate > the HW addressing scheme. > > Maybe this could never happen, or maybe it's not really important as the > pages there will be reserved anyway, but I'm not sure I can estimate all > the implications. >
I'm suggesting to let zone (+node?) ranges cover memory holes with a valid memmap. Not to move actual memory between nodes/zones.
-- Thanks,
David / dhildenb
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