[PATCH 13/13] x86/virt/tdx: Add tdx_guest_keyid_alloc/free() to alloc and free TDX guest KeyID

Paolo Bonzini
2025-01-01T07:50:27Z

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 6981a3d75eb2..c2fe56a3c7fa 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 84fe5bc79434..1a5912a8b5c5 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_pfn(td->tdr_page) << PAGE_SHIFT;
--
2.43.5