Re: [PATCHv5 23/30] x86/boot: Avoid #VE during boot for TDX platforms

[Xiaoyao Li]

On 3/2/2022 10:27 PM, Kirill A. Shutemov wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> There are a few MSRs and control register bits that the kernel
> normally needs to modify during boot. But, TDX disallows
> modification of these registers to help provide consistent security
> guarantees. Fortunately, TDX ensures that these are all in the correct
> state before the kernel loads, which means the kernel does not need to
> modify them.
>
> The conditions to avoid are:
>
>   * Any writes to the EFER MSR
>   * Clearing CR3.MCE

typo. CR4.MCE

BTW, I remember there was a patch to clear X86_FEATURE_MCE for TDX 
guest. Why does that get dropped?

Even though CPUID reports MCE is supported, all the access to MCE 
related MSRs causes #VE. If they are accessed via mce_rdmsrl(), the #VE 
will be fixed up and goes to ex_handler_msr_mce(). Finally lead to panic().