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

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Date: Wed, 6 Mar 2024 17:05:45 +0800
From: Yi Sun <yi.sun@...ux.intel.com>
To: isaku.yamahata@...el.com, Kai Huang <kai.huang@...el.com>,
	yi.sun@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
	erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, chen.bo@...el.com,
	hang.yuan@...el.com, tina.zhang@...el.com,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v19 005/130] x86/virt/tdx: Export global metadata read
 infrastructure

On 26.02.2024 00:25, isaku.yamahata@...el.com wrote:
>From: Kai Huang <kai.huang@...el.com>
>
>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@...el.com>
>Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>---
> 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