[PATCH] x86/kexec: Keep CR4.MCE during kexec for TDX guest

[Kirill A. Shutemov]

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, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 4a73351f87f8..9e83a638a2b8 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -145,8 +145,11 @@ 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	$X86_CR4_PAE, %eax
+	ALTERNATIVE "movl "$X86_CR4_PAE", %eax", \
+		    "movl "$(X86_CR4_PAE | X86_CR4_MCE)", %eax", X86_FEATURE_TDX_GUEST
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
-- 
  Kiryl Shutsemau / Kirill A. Shutemov