linux-kernel - Re: [PATCH v10 005/108] KVM: TDX: Initialize the TDX module when loading the KVM intel kernel module

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Date:   Tue, 8 Nov 2022 01:29:46 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v10 005/108] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module


> +
> +#define TDX_MAX_NR_CPUID_CONFIGS					\
> +	((sizeof(struct tdsysinfo_struct) -				\
> +		offsetof(struct tdsysinfo_struct, cpuid_configs))	\
> +		/ sizeof(struct tdx_cpuid_config))
> +
> +struct tdx_capabilities {
> +	u8 tdcs_nr_pages;
> +	u8 tdvpx_nr_pages;
> +
> +	u64 attrs_fixed0;
> +	u64 attrs_fixed1;
> +	u64 xfam_fixed0;
> +	u64 xfam_fixed1;
> +
> +	u32 nr_cpuid_configs;
> +	struct tdx_cpuid_config cpuid_configs[TDX_MAX_NR_CPUID_CONFIGS];
> +};
> +
> +/* Capabilities of KVM + the TDX module. */
> +static struct tdx_capabilities tdx_caps;

I think you can introduce this tdx_capabilities in another patch.

As claimed this patch can just focus on initializing the TDX module.  Whether
you need this tdx_capabilities or tdx_sysinfo is enough can be done in the patch
when they are really needed.  It makes review easier otherwise people won't be
able to tell why tdx_capabilities is needed here.

> +
> +static int __init tdx_module_setup(void)
> +{
> +	const struct tdsysinfo_struct *tdsysinfo;
> +	int ret = 0;
> +
> +	BUILD_BUG_ON(sizeof(*tdsysinfo) != 1024);
> +	BUILD_BUG_ON(TDX_MAX_NR_CPUID_CONFIGS != 37);
> +
> +	ret = tdx_enable();
> +	if (ret) {
> +		pr_info("Failed to initialize TDX module.\n");
> +		return ret;
> +	}
> +
> +	tdsysinfo = tdx_get_sysinfo();
> +	if (tdsysinfo->num_cpuid_config > TDX_MAX_NR_CPUID_CONFIGS)
> +		return -EIO;
> +
> +	tdx_caps = (struct tdx_capabilities) {
> +		.tdcs_nr_pages = tdsysinfo->tdcs_base_size / PAGE_SIZE,
> +		/*
> +		 * TDVPS = TDVPR(4K page) + TDVPX(multiple 4K pages).
> +		 * -1 for TDVPR.
> +		 */
> +		.tdvpx_nr_pages = tdsysinfo->tdvps_base_size / PAGE_SIZE - 1,
> +		.attrs_fixed0 = tdsysinfo->attributes_fixed0,
> +		.attrs_fixed1 = tdsysinfo->attributes_fixed1,
> +		.xfam_fixed0 =	tdsysinfo->xfam_fixed0,
> +		.xfam_fixed1 = tdsysinfo->xfam_fixed1,
> +		.nr_cpuid_configs = tdsysinfo->num_cpuid_config,
> +	};
> +	if (!memcpy(tdx_caps.cpuid_configs, tdsysinfo->cpuid_configs,
> +			tdsysinfo->num_cpuid_config *
> +			sizeof(struct tdx_cpuid_config)))
> +		return -EIO;
> +
> +	pr_info("kvm: TDX is supported. x86 phys bits %d\n",
> +		boot_cpu_data.x86_phys_bits);

What''s the benefit of print out x86_phys_bits?  Looks a little bit weird here.

TDX host code will print out TDX private KeyID range.  I think that is useful
enough?

> +
> +	return 0;
> +}
> +
> +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> +{
> +	int r;
> +
> +	if (!enable_ept) {
> +		pr_warn("Cannot enable TDX with EPT disabled\n");
> +		return -EINVAL;
> +	}
> +
> +	/* MOVDIR64B instruction is needed. */
> +	if (!static_cpu_has(X86_FEATURE_MOVDIR64B)) {
> +		pr_warn("Cannot enable TDX with MOVDIR64B supported ");
					   ^
					   without
> +		return -ENODEV;
> +	}

I think you should explain why MOVDIR64B is required, otherwise this just comes
out of blue.

Btw, is this absolutely required?  TDX also supports Li-mode, which doesn't have
integrity check.  So theoretically with Li-mode, normal zeroing is also OK but
doesn't need to use MOVDIR64B.

That being said, do we have a way to tell whether TDX works in Ci or Li mode?