On 30/11/2018 12:57, Kirill A. Shutemov wrote: > There is a guard hole at the beginning of kernel address space, also > used by hypervisors. It occupies 16 PGD entries. > > We do not state the reserved range directly, but calculate it relative > to other entities: direct mapping and user space ranges. > > The calculation got broken by recent change in kernel memory layout: LDT > remap range is now mapped before direct mapping and makes the calculation > invalid. > > The breakage leads to crash on Xen dom0 boot[1]. > > State the reserved range directly. It's part of kernel ABI (hypervisors > expect it to be stable) and must not depend on changes in the rest of > kernel memory layout. > > [1] https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg03313.html > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Reported-by: Hans van Kranenburg <Hans.van.Kranenburg@xxxxxxxxxx> > Fixes: d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on 5-level paging") > --- > arch/x86/include/asm/pgtable_64_types.h | 5 +++++ > arch/x86/mm/dump_pagetables.c | 8 ++++---- > arch/x86/xen/mmu_pv.c | 11 ++++++----- > 3 files changed, 15 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h > index 84bd9bdc1987..13aef22cee18 100644 > --- a/arch/x86/include/asm/pgtable_64_types.h > +++ b/arch/x86/include/asm/pgtable_64_types.h > @@ -111,6 +111,11 @@ extern unsigned int ptrs_per_p4d; > */ > #define MAXMEM (1UL << MAX_PHYSMEM_BITS) > > +#define GUARD_HOLE_PGD_ENTRY -256UL > +#define GUARD_HOLE_SIZE (16UL << PGDIR_SHIFT) > +#define GUARD_HOLE_BASE_ADDR (LDT_PGD_ENTRY << PGDIR_SHIFT) s/LDT_PGD_ENTRY/GUARD_HOLE_PGD_ENTRY/ Juergen
