[PATCH v14 014/113] x86/cpu: Add helper functions to allocate/free TDX private host key id

[isaku.yamahata@xxxxxxxxx]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Add helper functions to allocate/free TDX private host key id (HKID), and
export the global TDX HKID.

The memory controller encrypts TDX memory with the assigned TDX HKIDs.  The
global TDX HKID is to encrypt the TDX module, its memory, and some dynamic
data (TDR).  The private TDX HKID is assigned to guest TD to encrypt guest
memory and the related data.  When VMM releases an encrypted page for
reuse, the page needs a cache flush with the used HKID.  VMM needs the
global TDX HKID and the private TDX HKIDs to flush encrypted pages.

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/include/asm/tdx.h  | 12 ++++++++++++
 arch/x86/virt/vmx/tdx/tdx.c | 28 +++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 6c01ab572c1f..7d99a48a98cc 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -104,6 +104,16 @@ static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
 bool platform_tdx_enabled(void);
 int tdx_cpu_enable(void);
 int tdx_enable(void);
+/*
+ * Key id globally used by TDX module: TDX module maps TDR with this TDX global
+ * key id.  TDR includes key id assigned to the TD.  Then TDX module maps other
+ * TD-related pages with the assigned key id.  TDR requires this TDX global key
+ * id for cache flush unlike other TD-related pages.
+ */
+extern u32 tdx_global_keyid __ro_after_init;
+int tdx_guest_keyid_alloc(void);
+void tdx_guest_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 */
@@ -112,6 +122,8 @@ static inline int tdx_cpu_enable(void) { return -EINVAL; }
 static inline int tdx_enable(void)  { return -EINVAL; }
 static inline u64 __seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
 			     struct tdx_module_output *out) { return TDX_SEAMCALL_UD; };
+static inline int tdx_guest_keyid_alloc(void) { return -EOPNOTSUPP; }
+static inline void tdx_guest_keyid_free(int keyid) { }
 #endif	/* CONFIG_INTEL_TDX_HOST */
 
 #endif /* !__ASSEMBLY__ */
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index ee94a7327d93..511257086f02 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -33,7 +33,8 @@
 #include <asm/tdx.h>
 #include "tdx.h"
 
-static u32 tdx_global_keyid __ro_after_init;
+u32 tdx_global_keyid __ro_after_init;
+EXPORT_SYMBOL_GPL(tdx_global_keyid);
 static u32 tdx_guest_keyid_start __ro_after_init;
 static u32 tdx_nr_guest_keyids __ro_after_init;
 
@@ -138,6 +139,31 @@ static struct notifier_block tdx_memory_nb = {
 	.notifier_call = tdx_memory_notifier,
 };
 
+/* TDX KeyID pool */
+static DEFINE_IDA(tdx_guest_keyid_pool);
+
+int tdx_guest_keyid_alloc(void)
+{
+	if (WARN_ON_ONCE(!tdx_guest_keyid_start || !tdx_nr_guest_keyids))
+		return -EINVAL;
+
+	/* The first keyID is reserved for the global key. */
+	return ida_alloc_range(&tdx_guest_keyid_pool, tdx_guest_keyid_start + 1,
+			       tdx_guest_keyid_start + tdx_nr_guest_keyids - 1,
+			       GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(tdx_guest_keyid_alloc);
+
+void tdx_guest_keyid_free(int keyid)
+{
+	/* keyid = 0 is reserved. */
+	if (WARN_ON_ONCE(keyid <= 0))
+		return;
+
+	ida_free(&tdx_guest_keyid_pool, keyid);
+}
+EXPORT_SYMBOL_GPL(tdx_guest_keyid_free);
+
 static int __init tdx_init(void)
 {
 	u32 tdx_keyid_start, nr_tdx_keyids;
-- 
2.25.1