On Tue, Feb 27, 2018 at 06:42:14PM +0300, Kirill A. Shutemov wrote: > If a bootloader enables 64-bit mode with 4-level paging, we might need to > switch over to 5-level paging. The switching requires the disabling of > paging, which works fine if kernel itself is loaded below 4G. > > But if the bootloader puts the kernel above 4G (not sure if anybody does > this), we would lose control as soon as paging is disabled, because the > code becomes unreachable to the CPU. > > To handle the situation, we need a trampoline in lower memory that would > take care of switching on 5-level paging. > > This patch finds a spot in low memory for a trampoline. > > The heuristic is based on code in reserve_bios_regions(). > > We find the end of low memory based on BIOS and EBDA start addresses. > The trampoline is put just before end of low memory. It's mimic approach > taken to allocate memory for realtime trampoline. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Tested-by: Borislav Petkov <bp@xxxxxxx> > --- > arch/x86/boot/compressed/misc.c | 4 ++++ > arch/x86/boot/compressed/pgtable.h | 11 +++++++++++ > arch/x86/boot/compressed/pgtable_64.c | 34 ++++++++++++++++++++++++++++++++++ > 3 files changed, 49 insertions(+) > create mode 100644 arch/x86/boot/compressed/pgtable.h > > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c > index b50c42455e25..e58409667b13 100644 > --- a/arch/x86/boot/compressed/misc.c > +++ b/arch/x86/boot/compressed/misc.c > @@ -14,6 +14,7 @@ > > #include "misc.h" > #include "error.h" > +#include "pgtable.h" > #include "../string.h" > #include "../voffset.h" > > @@ -372,6 +373,9 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap, > debug_putaddr(output_len); > debug_putaddr(kernel_total_size); > > + /* Report address of 32-bit trampoline */ > + debug_putaddr(trampoline_32bit); > + > /* > * The memory hole needed for the kernel is the larger of either > * the entire decompressed kernel plus relocation table, or the 0-day found problem with the patch on 32-bit config. Here's fixup: diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c index e58409667b13..8e4b55dd5df9 100644 --- a/arch/x86/boot/compressed/misc.c +++ b/arch/x86/boot/compressed/misc.c @@ -373,8 +373,10 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap, debug_putaddr(output_len); debug_putaddr(kernel_total_size); +#ifdef CONFIG_X86_64 /* Report address of 32-bit trampoline */ debug_putaddr(trampoline_32bit); +#endif /* * The memory hole needed for the kernel is the larger of either -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
