Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory | Date | Mon, 1 Feb 2021 10:32:44 +0100 |
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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.
-- Thanks,
David / dhildenb
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