Re: [PATCH] x86/mm: Fix boot with some memory above MAXMEM

Mike Rapoport
2020-05-25T14:59:53Z

On Mon, May 25, 2020 at 07:49:02AM +0300, Kirill A. Shutemov wrote:
> 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@linux.intel.com>
> > Reviewed-by: Dave Hansen <dave.hansen@intel.com>
> > Cc: stable@vger.kernel.org # 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");

Could this happen at all when l5 is enabled?
Does it mean we need kmap() for 64-bit?

> > }
> >
> > /* Throw away partial pages: */
> > --
> > 2.26.2
> >
> >
>
> --
> Kirill A. Shutemov
>

--
Sincerely yours,
Mike.