Re: [RFC PATCH v2 1/4] KVM: x86: TDX: Track supported configurable CPUID bits

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The `tdx_cpu_cfg_cap_init` macro is highly fragile and relies on the caller providing a mandatory trailing comma, which will cause obscure syntax errors if omitted.
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commit 8aa0677abade944ac536d7acccef89b12ace7386
Author: Binbin Wu <binbin.wu@linux.intel.com>

KVM: x86: TDX: Track supported configurable CPUID bits

This patch introduces an allowlist for TDX directly configurable CPUID bits
supported by KVM. It tracks the supported bits by statically initializing
multi-bit fields and dynamically populating feature bits during hardware
setup using a new initialization macro.

> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index b8c3d3d8bbfe5..028d54c76b81e 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
[ ... ]
> @@ -52,6 +52,178 @@
> +#define TDX_F(name)					\
> +({							\
> +	tdx_cpu_cfg_caps |= feature_bit(name);		\
> +})
> +
> +#define tdx_cpu_cfg_cap_init(_func, _index, _reg, feature_initializers...)		\
> +do {											\
> +	u32 tdx_cpu_cfg_caps = 0;							\
> +											\
> +	for (int i = 0; i < ARRAY_SIZE(tdx_kvm_supported_cpuid); i++) {			\
> +		struct tdx_supported_cpuid_reg *r = &tdx_kvm_supported_cpuid[i];	\
> +											\
> +		if (r->function == _func && r->index == _index && r->reg == _reg) {	\
> +			feature_initializers						\
> +			r->mask |= tdx_cpu_cfg_caps;					\

[Severity: Low]
Is this macro design relying on the caller providing a mandatory trailing
comma?

Because feature_initializers expands to a list of statement expressions
like ({ tdx_cpu_cfg_caps |= feature_bit(name); }), omitting the trailing
comma in the macro invocation would result in a syntax error immediately
before r->mask |= tdx_cpu_cfg_caps.

Could TDX_F be redesigned to return the bitmask directly so they can be
combined using bitwise-OR, avoiding the strict trailing comma dependency?

> +			break;								\
> +		}									\
> +	}										\
> +											\
> +	WARN_ON_ONCE(!tdx_cpu_cfg_caps); 						\
> +} while (0)
> +
> +/* Only for TDX directly configurable CPUID feature bits */
> +static void __init tdx_initialize_cpu_cfg_caps(void)
> +{
> +	tdx_cpu_cfg_cap_init(0x1, 0, CPUID_ECX,
> +		TDX_F(MWAIT),
> +		TDX_F(TSC_DEADLINE_TIMER),
> +		TDX_F(AVX),
> +		TDX_F(F16C),
> +	);

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Sashiko AI review · https://sashiko.dev/#/patchset/20260604023314.3907511-1-binbin.wu@linux.intel.com?part=1