Message-ID: <aO4LVTvnsvt/UA+4@intel.com>
Date: Tue, 14 Oct 2025 16:35:33 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Rick P Edgecombe <rick.p.edgecombe@...el.com>, "x86@...nel.org"
	<x86@...nel.org>, "kas@...nel.org" <kas@...nel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"mingo@...hat.com" <mingo@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "bp@...en8.de" <bp@...en8.de>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, Kai Huang <kai.huang@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Dan J Williams
	<dan.j.williams@...el.com>, Adrian Hunter <adrian.hunter@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "xin@...or.com" <xin@...or.com>
Subject: Re: [RFC PATCH 3/4] KVM: x86/tdx: Do VMXON and TDX-Module
 initialization during tdx_init()

On Mon, Oct 13, 2025 at 01:59:21PM -0700, Sean Christopherson wrote:
>On Mon, Oct 13, 2025, Rick P Edgecombe wrote:
>> On Fri, 2025-10-10 at 15:04 -0700, Sean Christopherson wrote:
>> > @@ -3524,34 +3453,31 @@ static int __init __tdx_bringup(void)
>> >  	if (td_conf->max_vcpus_per_td < num_present_cpus()) {
>> >  		pr_err("Disable TDX: MAX_VCPU_PER_TD (%u) smaller than number of logical CPUs (%u).\n",
>> >  				td_conf->max_vcpus_per_td, num_present_cpus());
>> > -		goto get_sysinfo_err;
>> > +		return -EINVAL;
>> >  	}
>> >  
>> >  	if (misc_cg_set_capacity(MISC_CG_RES_TDX, tdx_get_nr_guest_keyids()))
>> > -		goto get_sysinfo_err;
>> > +		return -EINVAL;
>> >  
>> >  	/*
>> > -	 * Leave hardware virtualization enabled after TDX is enabled
>> > -	 * successfully.  TDX CPU hotplug depends on this.
>> > +	 * 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);
>> 
>> Could pass NULL instead of tdx_online_cpu() and delete this version of
>> tdx_online_cpu().
>
>Oh, nice, I didn't realize (or forgot) the startup call is optional.
> 
>> Also could remove the error handling too.
>
>No.  Partly on prinicple, but also because CPUHP_AP_ONLINE_DYN can fail if the
>kernel runs out of dynamic entries (currently limited to 40).  The kernel WARNs
>if it runs out of entries, but KVM should still do the right thing.
>
>> Also, can we name the two tdx_offline_cpu()'s differently? This one is all about
>> keyid's being in use. tdx_hkid_offline_cpu()?
>
>Ya.  And change the description to "kvm/cpu/tdx:hkid_packages"?  Or something
>like that.
>

Is it a good idea to consolidate the two tdx_offline_cpu() functions, i.e.,
integrate KVM's version into x86 core?

>From 97165f9933f48d588f5390e2d543d9880c03532d Mon Sep 17 00:00:00 2001
From: Chao Gao <chao.gao@...el.com>
Date: Tue, 14 Oct 2025 01:00:06 -0700
Subject: [PATCH] x86/virt/tdx: Consolidate TDX CPU hotplug handling

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@...el.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 d89382971076..beac8ab4cbc1 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -46,8 +46,6 @@ 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)
@@ -206,8 +204,6 @@ 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;
@@ -255,7 +251,6 @@ 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;
@@ -2487,8 +2482,6 @@ 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;
@@ -3343,51 +3336,10 @@ 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++) {
		/*
@@ -3459,23 +3411,7 @@ 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)
@@ -3531,7 +3467,6 @@ 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 bf1c1cdd9690..201ecb4ad20d 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;
 }
@@ -1505,15 +1541,22 @@ 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);
 
-- 
2.47.3

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