On Mon, May 11, 2020 at 10:17:21PM +0300, Kirill A. Shutemov wrote: > 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 > --- Gentle ping. It's not urgent, but it's a bug fix. Please consider applying. > 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 > > -- Kirill A. Shutemov
