TDX guests run with MCA enabled (CR4.MCE=1b) from the very start. If that bit is cleared during CR4 register reprogramming during boot or kexec flows, a #VE exception will be raised which the guest kernel cannot handle it. Therefore, make sure the CR4.MCE setting is preserved over kexec too and avoid raising any #VEs. The change doesn't affect non-TDX-guest environments. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> --- arch/x86/kernel/relocate_kernel_64.S | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S index 085eef5c3904..b668a6be4f6f 100644 --- a/arch/x86/kernel/relocate_kernel_64.S +++ b/arch/x86/kernel/relocate_kernel_64.S @@ -5,6 +5,8 @@ */ #include <linux/linkage.h> +#include <linux/stringify.h> +#include <asm/alternative.h> #include <asm/page_types.h> #include <asm/kexec.h> #include <asm/processor-flags.h> @@ -143,15 +145,17 @@ 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, if it was enabled before. + * Clearing MCE might not be allowed in TDX guests, depending on setup. + * - physical address extension enabled */ - movl $X86_CR4_PAE, %eax - testq $X86_CR4_LA57, %r13 - jz .Lno_la57 - orl $X86_CR4_LA57, %eax -.Lno_la57: + movl $X86_CR4_LA57, %eax + ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST + /* R13 contains the original CR4 value, read in relocate_kernel() */ + andl %r13d, %eax + orl $X86_CR4_PAE, %eax movq %rax, %cr4 jmp 1f -- 2.43.0
