On Fri, Mar 29, 2024 at 06:48:21PM +0200, Kirill A. Shutemov wrote: > On Fri, Mar 29, 2024 at 11:21:32PM +0800, Xiaoyao Li wrote: > > On 3/25/2024 6:38 PM, Kirill A. Shutemov wrote: > > > TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads > > > to #VE. > > > > Will we consider making it more safe and compatible for future to guard > > against X86_FEATURE_MCE as well? > > > > If in the future, MCE becomes configurable for TD guest, then CR4.MCE might > > not be fixed1. > > Good point. > > I guess we can leave it clear if it was clear. This should be easy > enough. But we might want to clear even if was set if clearing is allowed. > > It would require some kind of indication that clearing MCE is fine. We > don't have such indication yet. Not sure we can reasonably future-proof > the code at this point. > > But let me think more. I think I will go with the variant below. diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S index 56cab1bb25f5..8e2037d78a1f 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> @@ -145,11 +147,17 @@ 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 allowed in TDX guests, depending on setup. */ movl $X86_CR4_PAE, %eax testq $X86_CR4_LA57, %r13 jz 1f orl $X86_CR4_LA57, %eax +1: + testq $X86_CR4_MCE, %r13 + jz 1f + ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST 1: movq %rax, %cr4 -- Kiryl Shutsemau / Kirill A. Shutemov _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
