[PATCH 02/13] x86/virt/tdx: Add SEAMCALL wrappers for TDX TD creation

Paolo Bonzini
2025-01-01T07:50:13Z

From: Rick Edgecombe <rick.p.edgecombe@intel.com>

Intel TDX protects guest VMs from malicious hosts and certain physical
attacks. It defines various control structures that hold state for things
like TDs or vCPUs. These control structures are stored in pages given to
the TDX module and encrypted with either the global KeyID or the guest
KeyIDs.

To manipulate these control structures the TDX module defines a few
SEAMCALLs. KVM will use these during the process of creating a TD as
follows:

1) Allocate a unique TDX KeyID for a new guest.

1) Call TDH.MNG.CREATE to create a "TD Root" (TDR) page, together with
the new allocated KeyID. Unlike the rest of the TDX guest, the TDR
page is crypto-protected by the 'global KeyID'.

2) Call the previously added TDH.MNG.KEY.CONFIG on each package to
configure the KeyID for the guest. After this step, the KeyID to
protect the guest is ready and the rest of the guest will be protected
by this KeyID.

3) Call TDH.MNG.ADDCX to add TD Control Structure (TDCS) pages.

4) Call TDH.MNG.INIT to initialize the TDCS.

To reclaim these pages for use by the kernel other SEAMCALLs are needed,
which will be added in future patches.

Add tdh_mng_addcx(), tdh_mng_create() and tdh_mng_init() to export these
SEAMCALLs so that KVM can use them to create TDs.

For SEAMCALLs that give a page to the TDX module to be encrypted, CLFLUSH
the page mapped with KeyID 0, such that any dirty cache lines don't write
back later and clobber TD memory or control structures. Don't worry about
the other MK-TME KeyIDs because the kernel doesn't use them. The TDX docs
specify that this flush is not needed unless the TDX module exposes the
CLFLUSH_BEFORE_ALLOC feature bit. Be conservative and always flush. Add a
helper function to facilitate this.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Message-ID: <20241203010317.827803-3-rick.p.edgecombe@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/tdx.h | 3 +++
arch/x86/virt/vmx/tdx/tdx.c | 51 +++++++++++++++++++++++++++++++++++++
arch/x86/virt/vmx/tdx/tdx.h | 3 +++
3 files changed, 57 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 5045ab1c3d5b..425d282834e0 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -126,8 +126,11 @@ struct tdx_td {
struct page **tdcs_pages;
};

+u64 tdh_mng_addcx(struct tdx_td *td, struct page *tdcs_page);
u64 tdh_mng_key_config(struct tdx_td *td);
+u64 tdh_mng_create(struct tdx_td *td, u64 hkid);
u64 tdh_mng_key_freeid(struct tdx_td *td);
+u64 tdh_mng_init(struct tdx_td *td, u64 td_params, u64 *extended_err);
#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 55842d5b9474..c180551ecce3 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1462,6 +1462,29 @@ static inline u64 tdx_tdr_pa(struct tdx_td *td)
return page_to_pfn(td->tdr_page) << PAGE_SHIFT;
}

+/*
+ * The TDX module exposes a CLFLUSH_BEFORE_ALLOC bit to specify whether
+ * a CLFLUSH of pages is required before handing them to the TDX module.
+ * Be conservative and make the code simpler by doing the CLFLUSH
+ * unconditionally.
+ */
+static void tdx_clflush_page(struct page *tdr)
+{
+ clflush_cache_range(page_to_virt(tdr), PAGE_SIZE);
+}
+
+u64 tdh_mng_addcx(struct tdx_td *td, struct page *tdcs_page)
+{
+ struct tdx_module_args args = {
+ .rcx = page_to_pfn(tdcs_page) << PAGE_SHIFT,
+ .rdx = tdx_tdr_pa(td),
+ };
+
+ tdx_clflush_page(tdcs_page);
+ return seamcall(TDH_MNG_ADDCX, &args);
+}
+EXPORT_SYMBOL_GPL(tdh_mng_addcx);
+
u64 tdh_mng_key_config(struct tdx_td *td)
{
struct tdx_module_args args = {
@@ -1472,6 +1495,18 @@ u64 tdh_mng_key_config(struct tdx_td *td)
}
EXPORT_SYMBOL_GPL(tdh_mng_key_config);

+u64 tdh_mng_create(struct tdx_td *td, u64 hkid)
+{
+ struct tdx_module_args args = {
+ .rcx = tdx_tdr_pa(td),
+ .rdx = hkid,
+ };
+
+ tdx_clflush_page(td->tdr_page);
+ return seamcall(TDH_MNG_CREATE, &args);
+}
+EXPORT_SYMBOL_GPL(tdh_mng_create);
+
u64 tdh_mng_key_freeid(struct tdx_td *td)
{
struct tdx_module_args args = {
@@ -1481,3 +1516,19 @@ u64 tdh_mng_key_freeid(struct tdx_td *td)
return seamcall(TDH_MNG_KEY_FREEID, &args);
}
EXPORT_SYMBOL_GPL(tdh_mng_key_freeid);
+
+u64 tdh_mng_init(struct tdx_td *td, u64 td_params, u64 *extended_err)
+{
+ struct tdx_module_args args = {
+ .rcx = tdx_tdr_pa(td),
+ .rdx = td_params,
+ };
+ u64 ret;
+
+ ret = seamcall_ret(TDH_MNG_INIT, &args);
+
+ *extended_err = args.rcx;
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(tdh_mng_init);
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index 5579317f67ab..0861c3f09576 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -15,8 +15,11 @@
/*
* TDX module SEAMCALL leaf functions
*/
+#define TDH_MNG_ADDCX 1
#define TDH_MNG_KEY_CONFIG 8
+#define TDH_MNG_CREATE 9
#define TDH_MNG_KEY_FREEID 20
+#define TDH_MNG_INIT 21
#define TDH_PHYMEM_PAGE_RDMD 24
#define TDH_SYS_KEY_CONFIG 31
#define TDH_SYS_INIT 33
--
2.43.5