Re: [RFC PATCH v6 025/104] KVM: TDX: initialize VM with TDX specific parameters

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 5/6/2022 2:14 AM, isaku.yamahata@intel.com wrote:
> From: Xiaoyao Li <xiaoyao.li@intel.com>
> 
> TDX requires additional parameters for TDX VM for confidential execution to
> protect its confidentiality of its memory contents and its CPU state from
> any other software, including VMM. When creating guest TD VM before
> creating vcpu, the number of vcpu, TSC frequency (that is same among
> vcpus. and it can't be changed.)  CPUIDs which is emulated by the TDX
> module. It means guest can trust those CPUIDs. and sha384 values for
> measurement.
> 
> Add new subcommand, KVM_TDX_INIT_VM, to pass parameters for TDX guest.  It
> assigns encryption key to the TDX guest for memory encryption.  TDX
> encrypts memory per-guest bases.  It assigns device model passes per-VM
> parameters for the TDX guest.  The maximum number of vcpus, tsc frequency
> (TDX guest has fised VM-wide TSC frequency. not per-vcpu.  The TDX guest
> can not change it.), attributes (production or debug), available extended
> features (which is reflected into guest XCR0, IA32_XSS MSR), cpuids, sha384
> measurements, and etc.
> 
> This subcommand is called before creating vcpu and KVM_SET_CPUID2, i.e.
> cpuids configurations aren't available yet.  So CPUIDs configuration values
> needs to be passed in struct kvm_init_vm.  It's device model responsibility
> to make this cpuid config for KVM_TDX_INIT_VM and KVM_SET_CPUID2.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>   arch/x86/include/asm/kvm_host.h       |   2 +
>   arch/x86/include/uapi/asm/kvm.h       |  33 +++++
>   arch/x86/kvm/vmx/tdx.c                | 205 ++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/tdx.h                |  23 +++
>   tools/arch/x86/include/uapi/asm/kvm.h |  33 +++++
>   5 files changed, 296 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e6f6f8c8619f..bc2038157f11 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1250,6 +1250,8 @@ struct kvm_arch {
>   	 * the global KVM_MAX_VCPU_IDS may lead to significant memory waste.
>   	 */
>   	u32 max_vcpu_ids;
> +
> +	gfn_t gfn_shared_mask;
>   };
>   
>   struct kvm_vm_stat {
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index ca85a070ac19..0f067fe7c186 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -532,6 +532,7 @@ struct kvm_pmu_event_filter {
>   /* Trust Domain eXtension sub-ioctl() commands. */
>   enum kvm_tdx_cmd_id {
>   	KVM_TDX_CAPABILITIES = 0,
> +	KVM_TDX_INIT_VM,
>   
>   	KVM_TDX_CMD_NR_MAX,
>   };
> @@ -577,4 +578,36 @@ struct kvm_tdx_capabilities {
>   	struct kvm_tdx_cpuid_config cpuid_configs[0];
>   };
>   
> +struct kvm_tdx_init_vm {
> +	__u64 attributes;
> +	__u32 max_vcpus;
> +	__u32 tsc_khz;
> +	__u64 mrconfigid[6];	/* sha384 digest */
> +	__u64 mrowner[6];	/* sha384 digest */
> +	__u64 mrownerconfig[6];	/* sha348 digest */
> +	union {
> +		/*
> +		 * KVM_TDX_INIT_VM is called before vcpu creation, thus before
> +		 * KVM_SET_CPUID2.  CPUID configurations needs to be passed.
> +		 *
> +		 * This configuration supersedes KVM_SET_CPUID{,2}.
> +		 * The user space VMM, e.g. qemu, should make them consistent
> +		 * with this values.
> +		 * sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES(256)
> +		 * = 8KB.
> +		 */
> +		struct {
> +			struct kvm_cpuid2 cpuid;
> +			/* 8KB with KVM_MAX_CPUID_ENTRIES. */
> +			struct kvm_cpuid_entry2 entries[];
> +		};
> +		/*
> +		 * For future extensibility.
> +		 * The size(struct kvm_tdx_init_vm) = 16KB.
> +		 * This should be enough given sizeof(TD_PARAMS) = 1024
> +		 */
> +		__u64 reserved[2028];

I don't think it's a good idea to put the CPUID configs at the end of 
this structure and put it into a union.

1. The union makes the Array of Length zero entries[] pointless.
2. It wastes memory that when new field to be added in the future, it 
has to be put after union instead of inside union.

> +	};
> +};
> +
>   #endif /* _ASM_X86_KVM_H */
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index a4be3ef313b2..095ca7952114 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -438,6 +438,208 @@ int tdx_dev_ioctl(void __user *argp)
>   	return 0;
>   }
>   
> +#define TDX_CPUID_NO_INDEX	((u32)-1)

why do you bother introduing it in this version? I think we can use 0 
for those leaves without significant index as previous versions.

> +static const struct kvm_cpuid_entry2 *tdx_find_cpuid_entry(
> +	const struct kvm_tdx_init_vm *init_vm, u32 function, u32 index)
> +{
> +	int i;
> +
> +	for (i = 0; i < init_vm->cpuid.nent; i++) {
> +		const struct kvm_cpuid_entry2 *e = &init_vm->entries[i];
> +
> +		if (e->function == function &&
> +		    (e->index == index ||
> +		     !(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX)))
> +			return e;
> +	}
> +	return NULL;
> +}
> +
> +static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
> +			struct kvm_tdx_init_vm *init_vm)
> +{
> +	const struct kvm_cpuid_entry2 *entry;
> +	u64 guest_supported_xcr0;
> +	u64 guest_supported_xss;
> +	u32 guest_tsc_khz;
> +	int max_pa;
> +	int i;
> +
> +	td_params->max_vcpus = init_vm->max_vcpus;
> +
> +	td_params->attributes = init_vm->attributes;
> +	if (td_params->attributes & TDX_TD_ATTRIBUTE_PERFMON) {
> +		/*
> +		 * TODO: save/restore PMU related registers around TDENTER.
> +		 * Once it's done, remove this guard.
> +		 */
> +		pr_warn("TD doesn't support perfmon yet. KVM needs to save/restore "
> +			"host perf registers properly.\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	for (i = 0; i < tdx_caps.nr_cpuid_configs; i++) {
> +		const struct tdx_cpuid_config *config = &tdx_caps.cpuid_configs[i];
> +		const struct kvm_cpuid_entry2 *entry =
> +			tdx_find_cpuid_entry(init_vm, config->leaf, config->sub_leaf);
> +		struct tdx_cpuid_value *value = &td_params->cpuid_values[i];

why

	if (!entry)
		continue;

get lost in this version?

> +		value->eax = entry->eax & config->eax;
> +		value->ebx = entry->ebx & config->ebx;
> +		value->ecx = entry->ecx & config->ecx;
> +		value->edx = entry->edx & config->edx;
> +	}
> +
> +	max_pa = 36;
> +	entry = tdx_find_cpuid_entry(init_vm, 0x80000008, TDX_CPUID_NO_INDEX);
> +	if (entry)
> +		max_pa = entry->eax & 0xff;
> +
> +	td_params->eptp_controls = VMX_EPTP_MT_WB;
> +	/*
> +	 * No CPU supports 4-level && max_pa > 48.
> +	 * "5-level paging and 5-level EPT" section 4.1 4-level EPT
> +	 * "4-level EPT is limited to translating 48-bit guest-physical
> +	 *  addresses."
> +	 * cpu_has_vmx_ept_5levels() check is just in case.
> +	 */
> +	if (cpu_has_vmx_ept_5levels() && max_pa > 48) {
> +		td_params->eptp_controls |= VMX_EPTP_PWL_5;
> +		td_params->exec_controls |= TDX_EXEC_CONTROL_MAX_GPAW;
> +	} else {
> +		td_params->eptp_controls |= VMX_EPTP_PWL_4;
> +	}
> +
> +	/* Setup td_params.xfam */
> +	entry = tdx_find_cpuid_entry(init_vm, 0xd, 0);
> +	if (entry)
> +		guest_supported_xcr0 = (entry->eax | ((u64)entry->edx << 32));
> +	else
> +		guest_supported_xcr0 = 0;
> +	guest_supported_xcr0 &= supported_xcr0;
> +
> +	entry = tdx_find_cpuid_entry(init_vm, 0xd, 1);
> +	if (entry)
> +		guest_supported_xss = (entry->ecx | ((u64)entry->edx << 32));
> +	else
> +		guest_supported_xss = 0;
> +	/* PT can be exposed to TD guest regardless of KVM's XSS support */
> +	guest_supported_xss &= (supported_xss | XFEATURE_MASK_PT);
> +
> +	td_params->xfam = guest_supported_xcr0 | guest_supported_xss;
> +	if (td_params->xfam & XFEATURE_MASK_LBR) {
> +		/*
> +		 * TODO: once KVM supports LBR(save/restore LBR related
> +		 * registers around TDENTER), remove this guard.
> +		 */
> +		pr_warn("TD doesn't support LBR yet. KVM needs to save/restore "
> +			"IA32_LBR_DEPTH properly.\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (td_params->xfam & XFEATURE_MASK_XTILE) {
> +		/*
> +		 * TODO: once KVM supports AMX(save/restore AMX related
> +		 * registers around TDENTER), remove this guard.
> +		 */
> +		pr_warn("TD doesn't support AMX yet. KVM needs to save/restore "
> +			"IA32_XFD, IA32_XFD_ERR properly.\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (init_vm->tsc_khz) {
> +		guest_tsc_khz = init_vm->tsc_khz;
> +		kvm->arch.default_tsc_khz = guest_tsc_khz;
> +	} else
> +		guest_tsc_khz = kvm->arch.default_tsc_khz;
> +	td_params->tsc_frequency = TDX_TSC_KHZ_TO_25MHZ(guest_tsc_khz);
> +
> +#define MEMCPY_SAME_SIZE(dst, src)				\
> +	do {							\
> +		BUILD_BUG_ON(sizeof(dst) != sizeof(src));	\
> +		memcpy((dst), (src), sizeof(dst));		\
> +	} while (0)
> +
> +	MEMCPY_SAME_SIZE(td_params->mrconfigid, init_vm->mrconfigid);
> +	MEMCPY_SAME_SIZE(td_params->mrowner, init_vm->mrowner);
> +	MEMCPY_SAME_SIZE(td_params->mrownerconfig, init_vm->mrownerconfig);
> +
> +	return 0;
> +}
> +
> +static int tdx_td_init(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
> +{
> +	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> +	struct kvm_tdx_init_vm *init_vm = NULL;
> +	struct td_params *td_params = NULL;
> +	struct tdx_module_output out;
> +	int ret;
> +	u64 err;
> +
> +	BUILD_BUG_ON(sizeof(*init_vm) != 16 * 1024);
> +	BUILD_BUG_ON((sizeof(*init_vm) - offsetof(typeof(*init_vm), entries)) /
> +		     sizeof(init_vm->entries[0]) < KVM_MAX_CPUID_ENTRIES);
> +	BUILD_BUG_ON(sizeof(struct td_params) != 1024);
> +
> +	if (is_td_initialized(kvm))
> +		return -EINVAL;
> +
> +	if (cmd->flags)
> +		return -EINVAL;
> +
> +	init_vm = kzalloc(sizeof(*init_vm), GFP_KERNEL);
> +	if (copy_from_user(init_vm, (void __user *)cmd->data, sizeof(*init_vm))) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	if (init_vm->max_vcpus > KVM_MAX_VCPUS) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (tdx_caps.nr_cpuid_configs > KVM_MAX_CPUID_ENTRIES) {
> +		/* tdx_caps.nr_cpuis_configs should be smaller. */
> +		pr_warn("too large nr_cpuid_configs\n");
> +		ret = -E2BIG;
> +		goto out;
> +	}

No need to validate tdx_caps.nr_cpuid_configs here. It should and 
already has been validated when tdx_caps is setting up in tdx_module_setup()

> +
> +	td_params = kzalloc(sizeof(struct td_params), GFP_KERNEL);
> +	if (!td_params) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	ret = setup_tdparams(kvm, td_params, init_vm);
> +	if (ret)
> +		goto out;
> +
> +	err = tdh_mng_init(kvm_tdx->tdr.pa, __pa(td_params), &out);
> +	if (WARN_ON_ONCE(err)) {
> +		pr_tdx_error(TDH_MNG_INIT, err, &out);
> +		ret = -EIO;
> +		goto out;
> +	}
> +
> +	kvm_tdx->tsc_offset = td_tdcs_exec_read64(kvm_tdx, TD_TDCS_EXEC_TSC_OFFSET);
> +	kvm_tdx->attributes = td_params->attributes;
> +	kvm_tdx->xfam = td_params->xfam;
> +	kvm_tdx->tsc_khz = TDX_TSC_25MHZ_TO_KHZ(td_params->tsc_frequency);
> +	kvm->max_vcpus = td_params->max_vcpus;
> +
> +	if (td_params->exec_controls & TDX_EXEC_CONTROL_MAX_GPAW)
> +		kvm->arch.gfn_shared_mask = gpa_to_gfn(BIT_ULL(51));
> +	else
> +		kvm->arch.gfn_shared_mask = gpa_to_gfn(BIT_ULL(47));
> +
> +out:
> +	/* kfree() accepts NULL. */
> +	kfree(init_vm);
> +	kfree(td_params);
> +	return ret;
> +}
> +
>   int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
>   {
>   	struct kvm_tdx_cmd tdx_cmd;
> @@ -451,6 +653,9 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
>   	mutex_lock(&kvm->lock);
>   
>   	switch (tdx_cmd.id) {
> +	case KVM_TDX_INIT_VM:
> +		r = tdx_td_init(kvm, &tdx_cmd);
> +		break;
>   	default:
>   		r = -EINVAL;
>   		goto out;
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 8058b6b153f8..8a0793fcc3ab 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -20,7 +20,12 @@ struct kvm_tdx {
>   	struct tdx_td_page tdr;
>   	struct tdx_td_page *tdcs;
>   
> +	u64 attributes;
> +	u64 xfam;
>   	int hkid;
> +
> +	u64 tsc_offset;
> +	unsigned long tsc_khz;
>   };
>   
>   struct vcpu_tdx {
> @@ -50,6 +55,11 @@ static inline struct vcpu_tdx *to_tdx(struct kvm_vcpu *vcpu)
>   	return container_of(vcpu, struct vcpu_tdx, vcpu);
>   }
>   
> +static inline bool is_td_initialized(struct kvm *kvm)
> +{
> +	return !!kvm->max_vcpus;
> +}
> +
>   static __always_inline void tdvps_vmcs_check(u32 field, u8 bits)
>   {
>   	BUILD_BUG_ON_MSG(__builtin_constant_p(field) && (field) & 0x1,
> @@ -135,6 +145,19 @@ TDX_BUILD_TDVPS_ACCESSORS(64, VMCS, vmcs);
>   TDX_BUILD_TDVPS_ACCESSORS(64, STATE_NON_ARCH, state_non_arch);
>   TDX_BUILD_TDVPS_ACCESSORS(8, MANAGEMENT, management);
>   
> +static __always_inline u64 td_tdcs_exec_read64(struct kvm_tdx *kvm_tdx, u32 field)
> +{
> +	struct tdx_module_output out;
> +	u64 err;
> +
> +	err = tdh_mng_rd(kvm_tdx->tdr.pa, TDCS_EXEC(field), &out);
> +	if (unlikely(err)) {
> +		pr_err("TDH_MNG_RD[EXEC.0x%x] failed: 0x%llx\n", field, err);
> +		return 0;
> +	}
> +	return out.r8;
> +}
> +
>   #else
>   static inline int tdx_module_setup(void) { return -ENODEV; };
>   
> diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
> index a9ea3573be1b..779dfd683d66 100644
> --- a/tools/arch/x86/include/uapi/asm/kvm.h
> +++ b/tools/arch/x86/include/uapi/asm/kvm.h
> @@ -531,6 +531,7 @@ struct kvm_pmu_event_filter {
>   /* Trust Domain eXtension sub-ioctl() commands. */
>   enum kvm_tdx_cmd_id {
>   	KVM_TDX_CAPABILITIES = 0,
> +	KVM_TDX_INIT_VM,
>   
>   	KVM_TDX_CMD_NR_MAX,
>   };
> @@ -576,4 +577,36 @@ struct kvm_tdx_capabilities {
>   	struct kvm_tdx_cpuid_config cpuid_configs[0];
>   };
>   
> +struct kvm_tdx_init_vm {
> +	__u64 attributes;
> +	__u32 max_vcpus;
> +	__u32 tsc_khz;
> +	__u64 mrconfigid[6];    /* sha384 digest */
> +	__u64 mrowner[6];       /* sha384 digest */
> +	__u64 mrownerconfig[6]; /* sha348 digest */
> +	union {
> +		/*
> +		 * KVM_TDX_INIT_VM is called before vcpu creation, thus before
> +		 * KVM_SET_CPUID2.  CPUID configurations needs to be passed.
> +		 *
> +		 * This configuration supersedes KVM_SET_CPUID{,2}.
> +		 * The user space VMM, e.g. qemu, should make them consistent
> +		 * with this values.
> +		 * sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES(256)
> +		 * = 8KB.
> +		 */
> +		struct {
> +			struct kvm_cpuid2 cpuid;
> +			/* 8KB with KVM_MAX_CPUID_ENTRIES. */
> +			struct kvm_cpuid_entry2 entries[];
> +		};
> +		/*
> +		 * For future extensibility.
> +		 * The size(struct kvm_tdx_init_vm) = 16KB.
> +		 * This should be enough given sizeof(TD_PARAMS) = 1024
> +		 */
> +		__u64 reserved[2028];
> +	};
> +};
> +
>   #endif /* _ASM_X86_KVM_H */