tdx: derive TD ATTRIBUTES/XFAM from guest CPUID and validate GPAW

[liangzhou121]

tdx_filter_cpuid():

• Clear TSX (HLE bit 4 / RTM bit 11 in EBX) and WAITPKG (bit 5 in ECX) from CPUID leaf 7 subleaf 0, mirroring the kernel's tdx_clear_unsupported_cpuid().
• Encode the TD's GPAW in CPUID.0x80000008.EAX[23:16], the field KVM repurposes for setup_tdparams_eptp_controls(), and validate it is 48 or 52 before submitting it, instead of failing later with an opaque KVM_TDX_INIT_VM EINVAL.

tdx_init():

• Derive TD ATTRIBUTES (SEPT_VE_DISABLE, PKS, PERFMON) and XFAM from the guest CPUID view via new tdx_attributes_from_cpuid()/ tdx_xfam_from_cpuid() helpers, replacing the previous hardcoded attributes value (SEPT_VE_DISABLE only). Both are still masked to the configurable set reported by KVM_TDX_CAPABILITIES before being submitted to KVM_TDX_INIT_VM.

[Copilot]

🟡 Changes recommended

ATTRIBUTES/XFAM are currently derived from the unfiltered CPUID slice while KVM_TDX_INIT_VM is passed a filtered CPUID set, which can create inconsistencies and lead to EINVAL rejections.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR updates the TDX VM initialization flow to derive TD parameters from the guest CPUID view and to align CPUID filtering with what the TDX module/KVM expects, improving compatibility and making failures easier to diagnose.

Changes:

• Clear unsupported CPUID feature bits for TDX (TSX and WAITPKG) on leaf 7 subleaf 0.
• Preserve/encode and validate the TDX GPAW value via CPUID.0x80000008.EAX[23:16] before calling KVM_TDX_INIT_VM.
• Derive TD ATTRIBUTES and XFAM from CPUID via new helper functions and mask them against KVM_TDX_CAPABILITIES.

File summaries

File	Description
hypervisor/src/kvm/mod.rs	Updates TDX CPUID filtering and derives/masks TD ATTRIBUTES+XFAM for KVM_TDX_INIT_VM, including GPAW validation.

Review details

Suppressed comments (1)

hypervisor/src/kvm/mod.rs:1143

• This comment is grammatically incorrect and currently misleading: the code derives PERFMON/PKS from whatever CPUID slice is passed in. After switching the derivation to use the filtered CPUID view, update the wording to reflect that PERFMON is currently not requested because the filtered CPUID leaf 0xA is zeroed.

/// The PERFMON never set currently, `KVM_TDX_CAPABILITIES` reports
/// CPUID.(EAX=0xA) as all-zero, so `tdx_filter_cpuid()` always zeroes this
/// leaf before it reaches here.

• Files reviewed: 1/1 changed files
• Comments generated: 2
• Review effort level: Lite

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[guzongmin]

LGTM