[PATCH 05/13] x86/kexec: Keep CR4.MCE set during kexec for TDX guest
From: Kirill A. Shutemov
Date: Thu Oct 05 2023 - 11:58:29 EST
TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
to #VE.
Use alternatives to keep the flag during kexec for TDX guests.
The change doesn't affect non-TDX environments.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
arch/x86/kernel/relocate_kernel_64.S | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 56cab1bb25f5..bea89814b48e 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -145,11 +145,16 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
* Set cr4 to a known state:
* - physical address extension enabled
* - 5-level paging, if it was enabled before
+ * - Machine check exception on TDX guest. Clearing MCE is not allowed
+ * in TDX guests.
*/
movl $X86_CR4_PAE, %eax
testq $X86_CR4_LA57, %r13
jz 1f
orl $X86_CR4_LA57, %eax
+1:
+ ALTERNATIVE "jmp 1f", "", X86_FEATURE_TDX_GUEST
+ orl $X86_CR4_MCE, %eax
1:
movq %rax, %cr4
--
2.41.0