[PATCH v3 14/14] x86/virt/tdx: Add tdx_guest_keyid_alloc/free() to alloc and free TDX guest KeyID

[Paolo Bonzini <pbonzini@redhat.com>]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Intel TDX protects guest VMs from malicious host and certain physical
attacks. Pre-TDX Intel hardware has support for a memory encryption
architecture called MK-TME, which repurposes several high bits of
physical address as "KeyID". The BIOS reserves a sub-range of MK-TME
KeyIDs as "TDX private KeyIDs".

Each TDX guest must be assigned with a unique TDX KeyID when it is
created. The kernel reserves the first TDX private KeyID for
crypto-protection of specific TDX module data which has a lifecycle that
exceeds the KeyID reserved for the TD's use. The rest of the KeyIDs are
left for TDX guests to use.

Create a small KeyID allocator. Export
tdx_guest_keyid_alloc()/tdx_guest_keyid_free() to allocate and free TDX
guest KeyID for KVM to use.

Don't provide the stub functions when CONFIG_INTEL_TDX_HOST=n since they
are not supposed to be called in this case.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Message-ID: <20241030190039.77971-5-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 | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 6531b69a53ac..58182b245e36 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -117,6 +117,9 @@ int tdx_cpu_enable(void);
 int tdx_enable(void);
 const char *tdx_dump_mce_info(struct mce *m);
 
+int tdx_guest_keyid_alloc(void);
+void tdx_guest_keyid_free(unsigned int keyid);
+
 struct tdx_td {
 	/* TD root structure: */
 	struct page *tdr_page;
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index bb6f8ef9661e..bff350626b08 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -28,6 +28,7 @@
 #include <linux/log2.h>
 #include <linux/acpi.h>
 #include <linux/suspend.h>
+#include <linux/idr.h>
 #include <asm/page.h>
 #include <asm/special_insns.h>
 #include <asm/msr-index.h>
@@ -43,6 +44,8 @@ static u32 tdx_global_keyid __ro_after_init;
 static u32 tdx_guest_keyid_start __ro_after_init;
 static u32 tdx_nr_guest_keyids __ro_after_init;
 
+static DEFINE_IDA(tdx_guest_keyid_pool);
+
 static DEFINE_PER_CPU(bool, tdx_lp_initialized);
 
 static struct tdmr_info_list tdx_tdmr_list;
@@ -1458,6 +1461,20 @@ void __init tdx_init(void)
 	check_tdx_erratum();
 }
 
+int tdx_guest_keyid_alloc(void)
+{
+	return ida_alloc_range(&tdx_guest_keyid_pool, tdx_guest_keyid_start,
+			       tdx_guest_keyid_start + tdx_nr_guest_keyids - 1,
+			       GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(tdx_guest_keyid_alloc);
+
+void tdx_guest_keyid_free(unsigned int keyid)
+{
+	ida_free(&tdx_guest_keyid_pool, keyid);
+}
+EXPORT_SYMBOL_GPL(tdx_guest_keyid_free);
+
 static inline u64 tdx_tdr_pa(struct tdx_td *td)
 {
 	return page_to_phys(td->tdr_page);
-- 
2.43.5