[PATCH v2 5/7] x86/virt/tdx: KVM: Consolidate TDX CPU hotplug handling

Sean Christopherson
2025-12-06T01:11:16Z

From: Chao Gao <chao.gao@intel.com>

The core kernel registers a CPU hotplug callback to do VMX and TDX init
and deinit while KVM registers a separate CPU offline callback to block
offlining the last online CPU in a socket.

Splitting TDX-related CPU hotplug handling across two components is odd
and adds unnecessary complexity.

Consolidate TDX-related CPU hotplug handling by integrating KVM's
tdx_offline_cpu() to the one in the core kernel.

Also move nr_configured_hkid to the core kernel because tdx_offline_cpu()
references it. Since HKID allocation and free are handled in the core
kernel, it's more natural to track used HKIDs there.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/tdx.c | 67 +------------------------------------
arch/x86/virt/vmx/tdx/tdx.c | 49 +++++++++++++++++++++++++--
2 files changed, 47 insertions(+), 69 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index d0161dc3d184..d9dd6070baa0 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -59,8 +59,6 @@ module_param_named(tdx, enable_tdx, bool, 0444);
#define TDX_SHARED_BIT_PWL_5 gpa_to_gfn(BIT_ULL(51))
#define TDX_SHARED_BIT_PWL_4 gpa_to_gfn(BIT_ULL(47))

-static enum cpuhp_state tdx_cpuhp_state __ro_after_init;
-
static const struct tdx_sys_info *tdx_sysinfo;

void tdh_vp_rd_failed(struct vcpu_tdx *tdx, char *uclass, u32 field, u64 err)
@@ -219,8 +217,6 @@ static int init_kvm_tdx_caps(const struct tdx_sys_info_td_conf *td_conf,
*/
static DEFINE_MUTEX(tdx_lock);

-static atomic_t nr_configured_hkid;
-
static bool tdx_operand_busy(u64 err)
{
return (err & TDX_SEAMCALL_STATUS_MASK) == TDX_OPERAND_BUSY;
@@ -268,7 +264,6 @@ static inline void tdx_hkid_free(struct kvm_tdx *kvm_tdx)
{
tdx_guest_keyid_free(kvm_tdx->hkid);
kvm_tdx->hkid = -1;
- atomic_dec(&nr_configured_hkid);
misc_cg_uncharge(MISC_CG_RES_TDX, kvm_tdx->misc_cg, 1);
put_misc_cg(kvm_tdx->misc_cg);
kvm_tdx->misc_cg = NULL;
@@ -2399,8 +2394,6 @@ static int __tdx_td_init(struct kvm *kvm, struct td_params *td_params,

ret = -ENOMEM;

- atomic_inc(&nr_configured_hkid);
-
tdr_page = alloc_page(GFP_KERNEL);
if (!tdr_page)
goto free_hkid;
@@ -3302,51 +3295,10 @@ int tdx_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private)
return PG_LEVEL_4K;
}

-static int tdx_online_cpu(unsigned int cpu)
-{
- return 0;
-}
-
-static int tdx_offline_cpu(unsigned int cpu)
-{
- int i;
-
- /* No TD is running. Allow any cpu to be offline. */
- if (!atomic_read(&nr_configured_hkid))
- return 0;
-
- /*
- * In order to reclaim TDX HKID, (i.e. when deleting guest TD), need to
- * call TDH.PHYMEM.PAGE.WBINVD on all packages to program all memory
- * controller with pconfig. If we have active TDX HKID, refuse to
- * offline the last online cpu.
- */
- for_each_online_cpu(i) {
- /*
- * Found another online cpu on the same package.
- * Allow to offline.
- */
- if (i != cpu && topology_physical_package_id(i) ==
- topology_physical_package_id(cpu))
- return 0;
- }
-
- /*
- * This is the last cpu of this package. Don't offline it.
- *
- * Because it's hard for human operator to understand the
- * reason, warn it.
- */
-#define MSG_ALLPKG_ONLINE \
- "TDX requires all packages to have an online CPU. Delete all TDs in order to offline all CPUs of a package.\n"
- pr_warn_ratelimited(MSG_ALLPKG_ONLINE);
- return -EBUSY;
-}
-
static int __init __tdx_bringup(void)
{
const struct tdx_sys_info_td_conf *td_conf;
- int r, i;
+ int i;

for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
/*
@@ -3414,23 +3366,7 @@ static int __init __tdx_bringup(void)
if (misc_cg_set_capacity(MISC_CG_RES_TDX, tdx_get_nr_guest_keyids()))
return -EINVAL;

- /*
- * TDX-specific cpuhp callback to disallow offlining the last CPU in a
- * packing while KVM is running one or more TDs. Reclaiming HKIDs
- * requires doing PAGE.WBINVD on every package, i.e. offlining all CPUs
- * of a package would prevent reclaiming the HKID.
- */
- r = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "kvm/cpu/tdx:online",
- tdx_online_cpu, tdx_offline_cpu);
- if (r < 0)
- goto err_cpuhup;
-
- tdx_cpuhp_state = r;
return 0;
-
-err_cpuhup:
- misc_cg_set_capacity(MISC_CG_RES_TDX, 0);
- return r;
}

int __init tdx_bringup(void)
@@ -3486,7 +3422,6 @@ void tdx_cleanup(void)
return;

misc_cg_set_capacity(MISC_CG_RES_TDX, 0);
- cpuhp_remove_state(tdx_cpuhp_state);
}

void __init tdx_hardware_setup(void)
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index d49645797fe4..5cf008bffa94 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -58,6 +58,8 @@ static LIST_HEAD(tdx_memlist);
static struct tdx_sys_info tdx_sysinfo __ro_after_init;
static bool tdx_module_initialized __ro_after_init;

+static atomic_t nr_configured_hkid;
+
typedef void (*sc_err_func_t)(u64 fn, u64 err, struct tdx_module_args *args);

static inline void seamcall_err(u64 fn, u64 err, struct tdx_module_args *args)
@@ -190,6 +192,40 @@ static int tdx_online_cpu(unsigned int cpu)

static int tdx_offline_cpu(unsigned int cpu)
{
+ int i;
+
+ /* No TD is running. Allow any cpu to be offline. */
+ if (!atomic_read(&nr_configured_hkid))
+ goto done;
+
+ /*
+ * In order to reclaim TDX HKID, (i.e. when deleting guest TD), need to
+ * call TDH.PHYMEM.PAGE.WBINVD on all packages to program all memory
+ * controller with pconfig. If we have active TDX HKID, refuse to
+ * offline the last online cpu.
+ */
+ for_each_online_cpu(i) {
+ /*
+ * Found another online cpu on the same package.
+ * Allow to offline.
+ */
+ if (i != cpu && topology_physical_package_id(i) ==
+ topology_physical_package_id(cpu))
+ goto done;
+ }
+
+ /*
+ * This is the last cpu of this package. Don't offline it.
+ *
+ * Because it's hard for human operator to understand the
+ * reason, warn it.
+ */
+#define MSG_ALLPKG_ONLINE \
+ "TDX requires all packages to have an online CPU. Delete all TDs in order to offline all CPUs of a package.\n"
+ pr_warn_ratelimited(MSG_ALLPKG_ONLINE);
+ return -EBUSY;
+
+done:
x86_virt_put_cpu(X86_FEATURE_VMX);
return 0;
}
@@ -1506,15 +1542,22 @@ EXPORT_SYMBOL_GPL(tdx_get_nr_guest_keyids);

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);
+ int ret;
+
+ ret = ida_alloc_range(&tdx_guest_keyid_pool, tdx_guest_keyid_start,
+ tdx_guest_keyid_start + tdx_nr_guest_keyids - 1,
+ GFP_KERNEL);
+ if (ret >= 0)
+ atomic_inc(&nr_configured_hkid);
+
+ return ret;
}
EXPORT_SYMBOL_GPL(tdx_guest_keyid_alloc);

void tdx_guest_keyid_free(unsigned int keyid)
{
ida_free(&tdx_guest_keyid_pool, keyid);
+ atomic_dec(&nr_configured_hkid);
}
EXPORT_SYMBOL_GPL(tdx_guest_keyid_free);

--
2.52.0.223.gf5cc29aaa4-goog