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3548e131ec
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. Tested-by: Borislav Petkov <bp@suse.de> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Shevchenko <andy.shevchenko@gmail.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Eric Biederman <ebiederm@xmission.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20180226180451.86788-3-kirill.shutemov@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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