Mike Rapoport c351dc4d77 x86/setup: don't remove E820_TYPE_RAM for pfn 0 ... commit bde9cfa3afe4324ec251e4af80ebf9b7afaf7afe upstream. Patch series "mm: fix initialization of struct page for holes in memory layout", v3. Commit 73a6e474cb ("mm: memmap_init: iterate over memblock regions rather that check each PFN") exposed several issues with the memory map initialization and these patches fix those issues. Initially there were crashes during compaction that Qian Cai reported back in April [1]. It seemed back then that the problem was fixed, but a few weeks ago Andrea Arcangeli hit the same bug [2] and there was an additional discussion at [3]. [1] https://lore.kernel.org/lkml/8C537EB7-85EE-4DCF-943E-3CC0ED0DF56D@lca.pw [2] https://lore.kernel.org/lkml/20201121194506.13464-1-aarcange@redhat.com [3] https://lore.kernel.org/mm-commits/20201206005401.qKuAVgOXr%akpm@linux-foundation.org This patch (of 2): The first 4Kb of memory is a BIOS owned area and to avoid its allocation for the kernel it was not listed in e820 tables as memory. As the result, pfn 0 was never recognised by the generic memory management and it is not a part of neither node 0 nor ZONE_DMA. If set_pfnblock_flags_mask() would be ever called for the pageblock corresponding to the first 2Mbytes of memory, having pfn 0 outside of ZONE_DMA would trigger VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); Along with reserving the first 4Kb in e820 tables, several first pages are reserved with memblock in several places during setup_arch(). These reservations are enough to ensure the kernel does not touch the BIOS area and it is not necessary to remove E820_TYPE_RAM for pfn 0. Remove the update of e820 table that changes the type of pfn 0 and move the comment describing why it was done to trim_low_memory_range() that reserves the beginning of the memory. Link: https://lkml.kernel.org/r/20210111194017.22696-2-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Cc: Baoquan He <bhe@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: David Hildenbrand <david@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Qian Cai <cai@lca.pw> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2021-01-27 11:55:14 +01:00
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alpha
arc	arch/arc: add copy_user_page() to <asm/page.h> to fix build error on ARC	2021-01-19 18:27:26 +01:00
arm	xen: Fix event channel callback via INTX/GSI	2021-01-27 11:55:00 +01:00
arm64	arm64: entry: remove redundant IRQ flag tracing	2021-01-27 11:55:07 +01:00
c6x
csky
h8300
hexagon
ia64
m68k
microblaze
mips	MIPS: relocatable: fix possible boot hangup with KASLR enabled	2021-01-19 18:27:20 +01:00
nds32
nios2
openrisc
parisc
powerpc	powerpc/64s: fix scv entry fallback flush vs interrupt	2021-01-27 11:55:12 +01:00
riscv	RISC-V: Fix maximum allowed phsyical memory for RV32	2021-01-27 11:55:04 +01:00
s390
sh
sparc
um
x86	x86/setup: don't remove E820_TYPE_RAM for pfn 0	2021-01-27 11:55:14 +01:00
xtensa
.gitignore
Kconfig