On Tue, 2024-05-28 at 12:55 +0300, Kirill A. Shutemov wrote: > 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. Nit: the ending "it" isn't needed. > > 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> Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx> > --- > 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
