Re: [PATCH v2 16/25] KVM: TDX: Get system-wide info about TDX module on initialization

[Binbin Wu]

On 10/31/2024 3:00 AM, Rick Edgecombe wrote:
[...]
> +static u32 tdx_set_guest_phys_addr_bits(const u32 eax, int addr_bits)
> +{
> +	return (eax & ~GENMASK(23, 16)) | (addr_bits & 0xff) << 16;
> +}
> +
> +#define KVM_TDX_CPUID_NO_SUBLEAF	((__u32)-1)
> +
> +static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char idx)
> +{
> +	const struct tdx_sys_info_td_conf *td_conf = &tdx_sysinfo->td_conf;
> +
> +	entry->function = (u32)td_conf->cpuid_config_leaves[idx];
> +	entry->index = td_conf->cpuid_config_leaves[idx] >> 32;
> +	entry->eax = (u32)td_conf->cpuid_config_values[idx][0];
> +	entry->ebx = td_conf->cpuid_config_values[idx][0] >> 32;
> +	entry->ecx = (u32)td_conf->cpuid_config_values[idx][1];
> +	entry->edx = td_conf->cpuid_config_values[idx][1] >> 32;
> +
> +	if (entry->index == KVM_TDX_CPUID_NO_SUBLEAF)
> +		entry->index = 0;
> +
> +	/* Work around missing support on old TDX modules */
> +	if (entry->function == 0x80000008)
> +		entry->eax = tdx_set_guest_phys_addr_bits(entry->eax, 0xff);
Is it necessary to set bit 16~23 to 0xff?
It seems that when userspace wants to retrieve the value, the GPAW will
be set in tdx_read_cpuid() anyway.

> +}
> +
[...]