Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 29 Mar 2024 23:21:32 +0800 | Subject | Re: [PATCHv9 05/17] x86/kexec: Keep CR4.MCE set during kexec for TDX guest | From | Xiaoyao Li <> |
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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.
> Use alternatives to keep the flag during kexec for TDX guests. > > The change doesn't affect non-TDX-guest environments. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Reviewed-by: Kai Huang <kai.huang@intel.com> > Reviewed-by: Thomas Gleixner <tglx@linutronix.de> > --- > 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..e144bcf60cbe 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> > @@ -145,12 +147,15 @@ 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 "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST > movq %rax, %cr4 > > jmp 1f
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