Re: [RFC PATCH v2 4/4] KVM: x86: TDX: Report CORE_CAPABILITIES as supported

[Xiaoyao Li]

On 6/4/2026 10:33 AM, Binbin Wu wrote:
> Add CORE_CAPABILITIES (CPUID.0x7.0.EDX[30]) to the TDX configurable
> CPUID allowlist to accommodate legacy TDX module behavior.
>
> KVM doesn't support MSR_IA32_CORE_CAPS, however, some older TDX specs
> define CORE_CAPABILITIES CPUID bit as fixed-1.  As a result, userspace
> may expect this bit to be enabled in the TDX module for TDs.  When the
> CPUID bit becomes a directly configurable without reporting to the
> userspace, it can not be enabled.  To avoid confusing userspace, report
> CORE_CAPABILITIES to userspace via KVM_TDX_CAPABILITIES.
>
> Although KVM could determine the real CPUID setting by reading the
> metadata via SEAMCALL after KVM_TDX_INIT_VM, doing so is overkill to
> cover such a corner case.  If CORE_CAPABILITIES is exposed to a TDX
> guest, and the guest reads it, simply return 0.

shouldn't this patch be put as patch 02 instead of 04?

Patch 02 and 03 in this series break the old QEMU and then patch 04 
fixes the broken. This is not friendly to the bisect.