Re: [PATCH v19 111/130] KVM: TDX: Implement callbacks for MSR operations for TDX

Binbin Wu
2024-04-19T02:33:44Z

On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
>
> Implements set_msr/get_msr/has_emulated_msr methods for TDX to handle
> hypercall from guest TD for paravirtualized rdmsr and wrmsr. The TDX
> module virtualizes MSRs. For some MSRs, it injects #VE to the guest TD
> upon RDMSR or WRMSR. The exact list of such MSRs are defined in the spec.
>
> Upon #VE, the guest TD may execute hypercalls,
> TDG.VP.VMCALL<INSTRUCTION.RDMSR> and TDG.VP.VMCALL<INSTRUCTION.WRMSR>,
> which are defined in GHCI (Guest-Host Communication Interface) so that the
> host VMM (e.g. KVM) can virtualize the MSRs.
>
> There are three classes of MSRs virtualization.
> - non-configurable: TDX module directly virtualizes it. VMM can't
> configure. the value set by KVM_SET_MSR_INDEX_LIST is ignored.
> - configurable: TDX module directly virtualizes it. VMM can configure at
> the VM creation time. The value set by KVM_SET_MSR_INDEX_LIST is used.
> - #VE case
> Guest TD would issue TDG.VP.VMCALL<INSTRUCTION.{WRMSR,RDMSR> and
> VMM handles the MSR hypercall. The value set by KVM_SET_MSR_INDEX_LIST
> is used.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
[...]
> +
> +bool tdx_has_emulated_msr(u32 index, bool write)
> +{
> + switch (index) {
> + case MSR_IA32_UCODE_REV:
> + case MSR_IA32_ARCH_CAPABILITIES:
> + case MSR_IA32_POWER_CTL:
> + case MSR_IA32_CR_PAT:
> + case MSR_IA32_TSC_DEADLINE:
> + case MSR_IA32_MISC_ENABLE:
> + case MSR_PLATFORM_INFO:
> + case MSR_MISC_FEATURES_ENABLES:
> + case MSR_IA32_MCG_CAP:
> + case MSR_IA32_MCG_STATUS:
It not about this patch directly.

Intel SDM says:
"An attempt to write to IA32_MCG_STATUS with any value other than 0
would result in #GP".

But in set_msr_mce(), IA32_MCG_STATUS is set without any check.
Should it be checked against 0 if it is not host_initiated？