* Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > 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 prototype of trampoline_32bit should be in an #ifdef as well, as the variable only exists on 64-bit kernels. Thanks, Ingo -- 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>
