A 5-level paging capable machine can have memory above 46-bit in the physical address space. This memory is only addressable in the 5-level paging mode: we don't have enough virtual address space to create direct mapping for such memory in the 4-level paging mode. Currently, we fail boot completely: NULL pointer dereference in subsection_map_init(). Skip creating a memblock for such memory instead and notify user that some memory is not addressable. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # v4.14 --- Tested with a hacked QEMU: https://gist.github.com/kiryl/d45eb54110944ff95e544972d8bdac1d --- arch/x86/kernel/e820.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c index c5399e80c59c..d320d37d0f95 100644 --- a/arch/x86/kernel/e820.c +++ b/arch/x86/kernel/e820.c @@ -1280,8 +1280,8 @@ void __init e820__memory_setup(void) void __init e820__memblock_setup(void) { + u64 size, end, not_addressable = 0; int i; - u64 end; /* * The bootstrap memblock region count maximum is 128 entries @@ -1307,7 +1307,22 @@ void __init e820__memblock_setup(void) if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN) continue; - memblock_add(entry->addr, entry->size); + if (entry->addr >= MAXMEM) { + not_addressable += entry->size; + continue; + } + + end = min_t(u64, end, MAXMEM - 1); + size = end - entry->addr; + not_addressable += entry->size - size; + memblock_add(entry->addr, size); + } + + if (not_addressable) { + pr_err("%lldGB of physical memory is not addressable in the paging mode\n", + not_addressable >> 30); + if (!pgtable_l5_enabled()) + pr_err("Consider enabling 5-level paging\n"); } /* Throw away partial pages: */ -- 2.26.2
