4.14-stable review patch. If anyone has any objections, please let me know.
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From: Kirill A. Shutemov kirill.shutemov@linux.intel.com
commit 5bf30316991d5bcda046343ee77d823cf16fdd03 upstream.
Currently kexec() will crash when switching into a 5-level paging enabled kernel.
I missed that we need to change relocate_kernel() to set CR4.LA57 flag if the kernel has 5-level paging enabled.
I avoided using #ifdef CONFIG_X86_5LEVEL here and inferred if we need to enable 5-level paging from previous CR4 value. This way the code is ready for boot-time switching between paging modes.
With this patch applied, in addition to kexec 4-to-4 which always worked, we can kexec 4-to-5 and 5-to-5 - while 5-to-4 will need more work.
Reported-by: Baoquan He bhe@redhat.com Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Tested-by: Baoquan He bhe@redhat.com Cc: stable@vger.kernel.org # v4.14+ Cc: Borislav Petkov bp@suse.de Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-mm@kvack.org Fixes: 77ef56e4f0fb ("x86: Enable 5-level paging support via CONFIG_X86_5LEVEL=y") Link: http://lkml.kernel.org/r/20180129110845.26633-1-kirill.shutemov@linux.intel.... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/arch/x86/kernel/relocate_kernel_64.S +++ b/arch/x86/kernel/relocate_kernel_64.S @@ -68,6 +68,9 @@ relocate_kernel: movq %cr4, %rax movq %rax, CR4(%r11)
+ /* Save CR4. Required to enable the right paging mode later. */ + movq %rax, %r13 + /* zero out flags, and disable interrupts */ pushq $0 popfq @@ -126,8 +129,13 @@ identity_mapped: /* * Set cr4 to a known state: * - physical address extension enabled + * - 5-level paging, if it was enabled before */ movl $X86_CR4_PAE, %eax + testq $X86_CR4_LA57, %r13 + jz 1f + orl $X86_CR4_LA57, %eax +1: movq %rax, %cr4
jmp 1f