4.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kirill A. Shutemov <kirill.shute...@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 <b...@redhat.com>
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Tested-by: Baoquan He <b...@redhat.com>
Cc: <sta...@vger.kernel.org> # v4.14+
Cc: Borislav Petkov <b...@suse.de>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: linux...@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.shute...@linux.intel.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@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
