Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Mon, Oct 04, 2021 at 07:51:57PM -0700, Kuppuswamy Sathyanarayanan wrote:
> +/*
> + * Allocate it in the data region to avoid zeroing it during
> + * BSS initialization. It is mainly used in cc_platform_has()
> + * call during early boot call.
> + */
> +u64 __section(".data") is_tdx_guest = 0;

Actually this should be __ro_after_init, since it never changes after
it's initialized.  As a bonus you won't have to worry about it getting
placed in BSS and the comment and initializer can go away.

> +
> +static void __init is_tdx_guest_init(void)
> +{
> +	u32 eax, sig[3];
> +
> +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID) {
> +		is_tdx_guest = 0;
> +		return;
> +	}
> +
> +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
> +
> +	is_tdx_guest = !memcmp("IntelTDX    ", sig, 12);
> +}
> +
> +void __init tdx_early_init(void)
> +{
> +	is_tdx_guest_init();
> +
> +	if (!is_tdx_guest)
> +		return;
> +
> +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);

setup_force_cpu_cap() sets a bit in 'cpu_caps_set' which is in BSS,
which gets cleared later right?  So this presumably doesn't fully work
as expected.  Maybe it can be set in init_intel(), based on
'is_tdx_guest'.

-- 
Josh