Re: [PATCH v19 005/130] x86/virt/tdx: Export global metadata read infrastructure

[Yi Sun]

On 26.02.2024 00:25, isaku.yamahata@xxxxxxxxx wrote:
> From: Kai Huang <kai.huang@xxxxxxxxx>
>
> KVM will need to read a bunch of non-TDMR related metadata to create and
> run TDX guests.  Export the metadata read infrastructure for KVM to use.
>
> Specifically, export two helpers:
>
> 1) The helper which reads multiple metadata fields to a buffer of a
>   structure based on the "field ID -> structure member" mapping table.
>
> 2) The low level helper which just reads a given field ID.
>
> The two helpers cover cases when the user wants to cache a bunch of
> metadata fields to a certain structure and when the user just wants to
> query a specific metadata field on demand.  They are enough for KVM to
> use (and also should be enough for other potential users).
>
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
> arch/x86/include/asm/tdx.h  | 22 ++++++++++++++++++++++
> arch/x86/virt/vmx/tdx/tdx.c | 25 ++++++++-----------------
> 2 files changed, 30 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index eba178996d84..709b9483f9e4 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -116,6 +116,28 @@ static inline u64 sc_retry(sc_func_t func, u64 fn,
> int tdx_cpu_enable(void);
> int tdx_enable(void);
> const char *tdx_dump_mce_info(struct mce *m);
> +
> +struct tdx_metadata_field_mapping {
> +	u64 field_id;
> +	int offset;
> +	int size;
> +};
> +
> +#define TD_SYSINFO_MAP(_field_id, _struct, _member)	\
> +	{ .field_id = MD_FIELD_ID_##_field_id,		\
> +	  .offset   = offsetof(_struct, _member),	\
> +	  .size     = sizeof(typeof(((_struct *)0)->_member)) }
> +
> +/*
> + * Read multiple global metadata fields to a buffer of a structure
> + * based on the "field ID -> structure member" mapping table.
> + */
> +int tdx_sys_metadata_read(const struct tdx_metadata_field_mapping *fields,
> +			  int nr_fields, void *stbuf);
> +
> +/* Read a single global metadata field */
> +int tdx_sys_metadata_field_read(u64 field_id, u64 *data);
> +
> #else
> static inline void tdx_init(void) { }
> static inline int tdx_cpu_enable(void) { return -ENODEV; }
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index a19adc898df6..dc21310776ab 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -251,7 +251,7 @@ static int build_tdx_memlist(struct list_head *tmb_list)
> 	return ret;
> }
>
> -static int read_sys_metadata_field(u64 field_id, u64 *data)
> +int tdx_sys_metadata_field_read(u64 field_id, u64 *data)
> {
> 	struct tdx_module_args args = {};
> 	int ret;
> @@ -270,6 +270,7 @@ static int read_sys_metadata_field(u64 field_id, u64 *data)
>
> 	return 0;
> }
> +EXPORT_SYMBOL_GPL(tdx_sys_metadata_field_read);
>
> /* Return the metadata field element size in bytes */
> static int get_metadata_field_bytes(u64 field_id)
> @@ -295,7 +296,7 @@ static int stbuf_read_sys_metadata_field(u64 field_id,
> 	if (WARN_ON_ONCE(get_metadata_field_bytes(field_id) != bytes))
> 		return -EINVAL;
>
> -	ret = read_sys_metadata_field(field_id, &tmp);
> +	ret = tdx_sys_metadata_field_read(field_id, &tmp);
> 	if (ret)
> 		return ret;
>
> @@ -304,19 +305,8 @@ static int stbuf_read_sys_metadata_field(u64 field_id,
> 	return 0;
> }
>
> -struct field_mapping {
> -	u64 field_id;
> -	int offset;
> -	int size;
> -};
> -
> -#define TD_SYSINFO_MAP(_field_id, _struct, _member)	\
> -	{ .field_id = MD_FIELD_ID_##_field_id,		\
> -	  .offset   = offsetof(_struct, _member),	\
> -	  .size     = sizeof(typeof(((_struct *)0)->_member)) }
> -
> -static int read_sys_metadata(struct field_mapping *fields, int nr_fields,
> -			     void *stbuf)
> +int tdx_sys_metadata_read(const struct tdx_metadata_field_mapping *fields,
> +			  int nr_fields, void *stbuf)
> {
> 	int i, ret;
>
> @@ -331,6 +321,7 @@ static int read_sys_metadata(struct field_mapping *fields, int nr_fields,
>
> 	return 0;
> }
> +EXPORT_SYMBOL_GPL(tdx_sys_metadata_read);
Hi Kai,

The two helpers can potentially be used by TD guests, as you mentioned.
It's a good idea to declare it in the header asm/tdx.h.

However, the function cannot be compiled if its definition remains in the
vmx/tdx/tdx.c file while disabling the CONFIG_TDX_HOST.

It would be better to move the definition to a shared location,
allowing the host and guest to share the same code.

Thanks
  --Sun, Yi