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Subject[PATCH] x86/kexec: Make kexec work in 5-level paging mode
Date
I've missed that we need to change relocate_kernel() to set CR4.LA57
flag if the kernel has 5-level paging enabled.

I avoided to use ifdef CONFIG_X86_5LEVEL here and inferred if we need to
enabled 5-level paging from previous CR4 value. This way the code is
ready for boot-time switching between paging modes.

Fixes: 77ef56e4f0fb ("x86: Enable 5-level paging support via CONFIG_X86_5LEVEL=y")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Baoquan He <bhe@redhat.com>
---
arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 307d3bac5f04..11eda21eb697 100644
--- 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
--
2.15.1
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