Re: [PATCH v11 014/113] x86/virt/tdx: Add a helper function to return system wide info about TDX module

[Huang, Kai]

On Thu, 2023-01-12 at 08:31 -0800, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> TDX KVM needs system-wide information about the TDX module, struct
> tdsysinfo_struct.  Add a helper function tdx_get_sysinfo() to return it
> instead of KVM getting it with various error checks.  Make KVM call the
> function and stash the info.  Move out the struct definition about it to
> common place arch/x86/include/asm/tdx.h.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>  arch/x86/include/asm/tdx.h  | 54 +++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/vmx/tdx.c      | 49 ++++++++++++++++++++++++++++++++-
>  arch/x86/virt/vmx/tdx/tdx.c | 21 ++++++++++++---
>  arch/x86/virt/vmx/tdx/tdx.h | 51 -----------------------------------
>  4 files changed, 119 insertions(+), 56 deletions(-)
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index ed9cf61ff8b4..2ca6e8ce1e43 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -105,6 +105,58 @@ static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
>  #endif /* CONFIG_INTEL_TDX_GUEST && CONFIG_KVM_GUEST */
>  
>  #ifdef CONFIG_INTEL_TDX_HOST
> +struct tdx_cpuid_config {
> +	u32	leaf;
> +	u32	sub_leaf;
> +	u32	eax;
> +	u32	ebx;
> +	u32	ecx;
> +	u32	edx;
> +} __packed;
> +
> +#define TDSYSINFO_STRUCT_SIZE		1024
> +#define TDSYSINFO_STRUCT_ALIGNMENT	1024
> +
> +/*
> + * The size of this structure itself is flexible.  The actual structure
> + * passed to TDH.SYS.INFO must be padded to TDSYSINFO_STRUCT_SIZE and be
> + * aligned to TDSYSINFO_STRUCT_ALIGNMENT using DECLARE_PADDED_STRUCT().
> + */
> +struct tdsysinfo_struct {
> +	/* TDX-SEAM Module Info */
> +	u32	attributes;
> +	u32	vendor_id;
> +	u32	build_date;
> +	u16	build_num;
> +	u16	minor_version;
> +	u16	major_version;
> +	u8	reserved0[14];
> +	/* Memory Info */
> +	u16	max_tdmrs;
> +	u16	max_reserved_per_tdmr;
> +	u16	pamt_entry_size;
> +	u8	reserved1[10];
> +	/* Control Struct Info */
> +	u16	tdcs_base_size;
> +	u8	reserved2[2];
> +	u16	tdvps_base_size;
> +	u8	tdvps_xfam_dependent_size;
> +	u8	reserved3[9];
> +	/* TD Capabilities */
> +	u64	attributes_fixed0;
> +	u64	attributes_fixed1;
> +	u64	xfam_fixed0;
> +	u64	xfam_fixed1;
> +	u8	reserved4[32];
> +	u32	num_cpuid_config;
> +	/*
> +	 * The actual number of CPUID_CONFIG depends on above
> +	 * 'num_cpuid_config'.
> +	 */
> +	DECLARE_FLEX_ARRAY(struct tdx_cpuid_config, cpuid_configs);
> +} __packed;
> +
> +const struct tdsysinfo_struct *tdx_get_sysinfo(void);
>  bool platform_tdx_enabled(void);
>  int tdx_enable(void);
>  /*
> @@ -120,6 +172,8 @@ void tdx_keyid_free(int keyid);
>  u64 __seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
>  	       struct tdx_module_output *out);
>  #else	/* !CONFIG_INTEL_TDX_HOST */
> +struct tdsysinfo_struct;
> +static inline const struct tdsysinfo_struct *tdx_get_sysinfo(void) { return NULL; }
>  static inline bool platform_tdx_enabled(void) { return false; }
>  static inline int tdx_enable(void)  { return -EINVAL; }
>  static inline int tdx_keyid_alloc(void) { return -EOPNOTSUPP; }
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 6c7d9ec53046..2adf5551ab26 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -11,9 +11,34 @@
>  #undef pr_fmt
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
> +#define TDX_MAX_NR_CPUID_CONFIGS					\
> +	((TDSYSINFO_STRUCT_SIZE -					\
> +		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;
> +
>  static int __init tdx_module_setup(void)
>  {
> -	int ret;
> +	const struct tdsysinfo_struct *tdsysinfo;
> +	int ret = 0;
> +
> +	BUILD_BUG_ON(sizeof(*tdsysinfo) > TDSYSINFO_STRUCT_SIZE);
> +	BUILD_BUG_ON(TDX_MAX_NR_CPUID_CONFIGS != 37);
>  
>  	ret = tdx_enable();
>  	if (ret) {
> @@ -21,6 +46,28 @@ static int __init tdx_module_setup(void)
>  		return ret;
>  	}
>  
> +	tdsysinfo = tdx_get_sysinfo();
> +	if (tdsysinfo->num_cpuid_config > TDX_MAX_NR_CPUID_CONFIGS)
> +		return -EIO;

This check basically means TDX module is buggy (or kernel has bug).  Do we
really need this check?  Is TDX module that buggy?

IMHO you don't need this one, or use WARN() if you want to catch kernel bug?

> +
> +	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;

Why introducing 'struct tdx_capabilities' and above code here in this patch?

It's entirely not clear why the new structure is needed -- nothing mentioned in
changelog, nor there's any comment.  Please explain in the changelog or move
this chunk to where it is needed.

Technical side, is 'struct tdx_capabilities' really needed? Or is it just for
convenience?

[snip]