Date: Sun, 7 Apr 2024 17:03:26 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v19 087/130] KVM: TDX: handle vcpu migration over logical
 processor



On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> For vcpu migration, in the case of VMX, VMCS is flushed on the source pcpu,
> and load it on the target pcpu.  There are corresponding TDX SEAMCALL APIs,
> call them on vcpu migration.  The logic is mostly same as VMX except the
> TDX SEAMCALLs are used.
>
> When shutting down the machine,

"the machine" -> "a VM"

>   (VMX or TDX) vcpus needs to be shutdown on
                    ^
                    need
> each pcpu.  Do the similar for TDX with TDX SEAMCALL APIs.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/kvm/vmx/main.c    |  32 ++++++-
>   arch/x86/kvm/vmx/tdx.c     | 190 ++++++++++++++++++++++++++++++++++++-
>   arch/x86/kvm/vmx/tdx.h     |   2 +
>   arch/x86/kvm/vmx/x86_ops.h |   4 +
>   4 files changed, 221 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 8275a242ce07..9b336c1a6508 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -33,6 +33,14 @@ static int vt_max_vcpus(struct kvm *kvm)
>   static int vt_flush_remote_tlbs(struct kvm *kvm);
>   #endif
>   
> +static void vt_hardware_disable(void)
> +{
> +	/* Note, TDX *and* VMX need to be disabled if TDX is enabled. */
> +	if (enable_tdx)
> +		tdx_hardware_disable();
> +	vmx_hardware_disable();
> +}
> +
>   static __init int vt_hardware_setup(void)
>   {
>   	int ret;
> @@ -201,6 +209,16 @@ static fastpath_t vt_vcpu_run(struct kvm_vcpu *vcpu)
>   	return vmx_vcpu_run(vcpu);
>   }
>   
> +static void vt_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> +{
> +	if (is_td_vcpu(vcpu)) {
> +		tdx_vcpu_load(vcpu, cpu);
> +		return;
> +	}
> +
> +	vmx_vcpu_load(vcpu, cpu);
> +}
> +
>   static void vt_flush_tlb_all(struct kvm_vcpu *vcpu)
>   {
>   	if (is_td_vcpu(vcpu)) {
> @@ -262,6 +280,14 @@ static void vt_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
>   	vmx_load_mmu_pgd(vcpu, root_hpa, pgd_level);
>   }
>   
> +static void vt_sched_in(struct kvm_vcpu *vcpu, int cpu)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return;
> +
> +	vmx_sched_in(vcpu, cpu);
> +}
> +
>   static u8 vt_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
>   {
>   	if (is_td_vcpu(vcpu))
> @@ -335,7 +361,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>   
>   	/* TDX cpu enablement is done by tdx_hardware_setup(). */
>   	.hardware_enable = vmx_hardware_enable,
> -	.hardware_disable = vmx_hardware_disable,
> +	.hardware_disable = vt_hardware_disable,
>   	.has_emulated_msr = vmx_has_emulated_msr,
>   
>   	.is_vm_type_supported = vt_is_vm_type_supported,
> @@ -353,7 +379,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>   	.vcpu_reset = vt_vcpu_reset,
>   
>   	.prepare_switch_to_guest = vt_prepare_switch_to_guest,
> -	.vcpu_load = vmx_vcpu_load,
> +	.vcpu_load = vt_vcpu_load,
>   	.vcpu_put = vt_vcpu_put,
>   
>   	.update_exception_bitmap = vmx_update_exception_bitmap,
> @@ -440,7 +466,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>   
>   	.request_immediate_exit = vmx_request_immediate_exit,
>   
> -	.sched_in = vmx_sched_in,
> +	.sched_in = vt_sched_in,
>   
>   	.cpu_dirty_log_size = PML_ENTITY_NUM,
>   	.update_cpu_dirty_logging = vmx_update_cpu_dirty_logging,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index ad4d3d4eaf6c..7aa9188f384d 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -106,6 +106,14 @@ static DEFINE_MUTEX(tdx_lock);
>   static struct mutex *tdx_mng_key_config_lock;
>   static atomic_t nr_configured_hkid;
>   
> +/*
> + * A per-CPU list of TD vCPUs associated with a given CPU.  Used when a CPU
> + * is brought down

Not necessarily to be a CPU brought down.
It will also be triggered by the last VM being destroyed.

But had a seond thought, if it is trigged by the last VM case, the list 
should be empty already.
So I am OK with the descripton.


>   to invoke TDH_VP_FLUSH on the approapriate TD vCPUS.

"approapriate" -> "appropriate"

> + * Protected by interrupt mask.  This list is manipulated in process context
> + * of vcpu and IPI callback.  See tdx_flush_vp_on_cpu().
> + */
> +static DEFINE_PER_CPU(struct list_head, associated_tdvcpus);
> +
>   static __always_inline hpa_t set_hkid_to_hpa(hpa_t pa, u16 hkid)
>   {
>   	return pa | ((hpa_t)hkid << boot_cpu_data.x86_phys_bits);
> @@ -138,6 +146,37 @@ static inline bool is_td_finalized(struct kvm_tdx *kvm_tdx)
>   	return kvm_tdx->finalized;
>   }
>   
> +static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
> +{
> +	lockdep_assert_irqs_disabled();
> +
> +	list_del(&to_tdx(vcpu)->cpu_list);
> +
> +	/*
> +	 * Ensure tdx->cpu_list is updated is before setting vcpu->cpu to -1,
> +	 * otherwise, a different CPU can see vcpu->cpu = -1 and add the vCPU
> +	 * to its list before its deleted from this CPUs list.
> +	 */
> +	smp_wmb();
> +
> +	vcpu->cpu = -1;
> +}
> +
> +static void tdx_disassociate_vp_arg(void *vcpu)
> +{
> +	tdx_disassociate_vp(vcpu);
> +}
> +
> +static void tdx_disassociate_vp_on_cpu(struct kvm_vcpu *vcpu)
> +{
> +	int cpu = vcpu->cpu;
> +
> +	if (unlikely(cpu == -1))
> +		return;
> +
> +	smp_call_function_single(cpu, tdx_disassociate_vp_arg, vcpu, 1);
> +}
> +
>   static void tdx_clear_page(unsigned long page_pa)
>   {
>   	const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
> @@ -218,6 +257,87 @@ static void tdx_reclaim_control_page(unsigned long td_page_pa)
>   	free_page((unsigned long)__va(td_page_pa));
>   }
>   
> +struct tdx_flush_vp_arg {
> +	struct kvm_vcpu *vcpu;
> +	u64 err;
> +};
> +
> +static void tdx_flush_vp(void *arg_)

It is more common to use "_arg" instead of "arg_".

> +{
> +	struct tdx_flush_vp_arg *arg = arg_;
> +	struct kvm_vcpu *vcpu = arg->vcpu;
> +	u64 err;
> +
> +	arg->err = 0;
> +	lockdep_assert_irqs_disabled();
> +
> +	/* Task migration can race with CPU offlining. */
> +	if (unlikely(vcpu->cpu != raw_smp_processor_id()))
> +		return;
> +
> +	/*
> +	 * No need to do TDH_VP_FLUSH if the vCPU hasn't been initialized.  The
> +	 * list tracking still needs to be updated so that it's correct if/when
> +	 * the vCPU does get initialized.
> +	 */
> +	if (is_td_vcpu_created(to_tdx(vcpu))) {
> +		/*
> +		 * No need to retry.  TDX Resources needed for TDH.VP.FLUSH are,
> +		 * TDVPR as exclusive, TDR as shared, and TDCS as shared.  This
> +		 * vp flush function is called when destructing vcpu/TD or vcpu
> +		 * migration.  No other thread uses TDVPR in those cases.
> +		 */
> +		err = tdh_vp_flush(to_tdx(vcpu)->tdvpr_pa);
> +		if (unlikely(err && err != TDX_VCPU_NOT_ASSOCIATED)) {
> +			/*
> +			 * This function is called in IPI context. Do not use
> +			 * printk to avoid console semaphore.
> +			 * The caller prints out the error message, instead.
> +			 */
> +			if (err)
> +				arg->err = err;
> +		}
> +	}
> +
> +	tdx_disassociate_vp(vcpu);
> +}
> +
> +static void tdx_flush_vp_on_cpu(struct kvm_vcpu *vcpu)
> +{
> +	struct tdx_flush_vp_arg arg = {
> +		.vcpu = vcpu,
> +	};
> +	int cpu = vcpu->cpu;
> +
> +	if (unlikely(cpu == -1))
> +		return;
> +
> +	smp_call_function_single(cpu, tdx_flush_vp, &arg, 1);
> +	if (WARN_ON_ONCE(arg.err)) {
> +		pr_err("cpu: %d ", cpu);
> +		pr_tdx_error(TDH_VP_FLUSH, arg.err, NULL);
> +	}
> +}
> +
> +void tdx_hardware_disable(void)
> +{
> +	int cpu = raw_smp_processor_id();
> +	struct list_head *tdvcpus = &per_cpu(associated_tdvcpus, cpu);
> +	struct tdx_flush_vp_arg arg;
> +	struct vcpu_tdx *tdx, *tmp;
> +	unsigned long flags;
> +
> +	lockdep_assert_preemption_disabled();
> +
> +	local_irq_save(flags);
> +	/* Safe variant needed as tdx_disassociate_vp() deletes the entry. */
> +	list_for_each_entry_safe(tdx, tmp, tdvcpus, cpu_list) {
> +		arg.vcpu = &tdx->vcpu;
> +		tdx_flush_vp(&arg);
> +	}
> +	local_irq_restore(flags);
> +}
> +
>   static void tdx_do_tdh_phymem_cache_wb(void *unused)
>   {
>   	u64 err = 0;
> @@ -233,26 +353,31 @@ static void tdx_do_tdh_phymem_cache_wb(void *unused)
>   		pr_tdx_error(TDH_PHYMEM_CACHE_WB, err, NULL);
>   }
>   
> -void tdx_mmu_release_hkid(struct kvm *kvm)
> +static int __tdx_mmu_release_hkid(struct kvm *kvm)
>   {
>   	bool packages_allocated, targets_allocated;
>   	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
>   	cpumask_var_t packages, targets;
> +	struct kvm_vcpu *vcpu;
> +	unsigned long j;
> +	int i, ret = 0;
>   	u64 err;
> -	int i;
>   
>   	if (!is_hkid_assigned(kvm_tdx))
> -		return;
> +		return 0;
>   
>   	if (!is_td_created(kvm_tdx)) {
>   		tdx_hkid_free(kvm_tdx);
> -		return;
> +		return 0;
>   	}
>   
>   	packages_allocated = zalloc_cpumask_var(&packages, GFP_KERNEL);
>   	targets_allocated = zalloc_cpumask_var(&targets, GFP_KERNEL);
>   	cpus_read_lock();
>   
> +	kvm_for_each_vcpu(j, vcpu, kvm)
> +		tdx_flush_vp_on_cpu(vcpu);
> +
>   	/*
>   	 * We can destroy multiple guest TDs simultaneously.  Prevent
>   	 * tdh_phymem_cache_wb from returning TDX_BUSY by serialization.
> @@ -270,6 +395,19 @@ void tdx_mmu_release_hkid(struct kvm *kvm)
>   	 */
>   	write_lock(&kvm->mmu_lock);
>   
> +	err = tdh_mng_vpflushdone(kvm_tdx->tdr_pa);
> +	if (err == TDX_FLUSHVP_NOT_DONE) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +	if (WARN_ON_ONCE(err)) {
> +		pr_tdx_error(TDH_MNG_VPFLUSHDONE, err, NULL);
> +		pr_err("tdh_mng_vpflushdone() failed. HKID %d is leaked.\n",
> +		       kvm_tdx->hkid);
> +		ret = -EIO;
> +		goto out;
> +	}
> +
>   	for_each_online_cpu(i) {
>   		if (packages_allocated &&
>   		    cpumask_test_and_set_cpu(topology_physical_package_id(i),
> @@ -291,14 +429,24 @@ void tdx_mmu_release_hkid(struct kvm *kvm)
>   		pr_tdx_error(TDH_MNG_KEY_FREEID, err, NULL);
>   		pr_err("tdh_mng_key_freeid() failed. HKID %d is leaked.\n",
>   		       kvm_tdx->hkid);
> +		ret = -EIO;
>   	} else
>   		tdx_hkid_free(kvm_tdx);
>   
> +out:
>   	write_unlock(&kvm->mmu_lock);
>   	mutex_unlock(&tdx_lock);
>   	cpus_read_unlock();
>   	free_cpumask_var(targets);
>   	free_cpumask_var(packages);
> +
> +	return ret;
> +}
> +
> +void tdx_mmu_release_hkid(struct kvm *kvm)
> +{
> +	while (__tdx_mmu_release_hkid(kvm) == -EBUSY)
> +		;
>   }
>   
>   void tdx_vm_free(struct kvm *kvm)
> @@ -455,6 +603,26 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
>   	return 0;
>   }
>   
> +void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> +{
> +	struct vcpu_tdx *tdx = to_tdx(vcpu);
> +
> +	if (vcpu->cpu == cpu)
> +		return;
> +
> +	tdx_flush_vp_on_cpu(vcpu);
> +
> +	local_irq_disable();
> +	/*
> +	 * Pairs with the smp_wmb() in tdx_disassociate_vp() to ensure
> +	 * vcpu->cpu is read before tdx->cpu_list.
> +	 */
> +	smp_rmb();
> +
> +	list_add(&tdx->cpu_list, &per_cpu(associated_tdvcpus, cpu));
> +	local_irq_enable();
> +}
> +
>   void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>   {
>   	struct vcpu_tdx *tdx = to_tdx(vcpu);
> @@ -495,6 +663,16 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu)
>   	struct vcpu_tdx *tdx = to_tdx(vcpu);
>   	int i;
>   
> +	/*
> +	 * When destroying VM, kvm_unload_vcpu_mmu() calls vcpu_load() for every
> +	 * vcpu after they already disassociated from the per cpu list by
> +	 * tdx_mmu_release_hkid().  So we need to disassociate them again,
> +	 * otherwise the freed vcpu data will be accessed when do
> +	 * list_{del,add}() on associated_tdvcpus list later.
> +	 */
> +	tdx_disassociate_vp_on_cpu(vcpu);
> +	WARN_ON_ONCE(vcpu->cpu != -1);
> +
>   	/*
>   	 * This methods can be called when vcpu allocation/initialization
>   	 * failed. So it's possible that hkid, tdvpx and tdvpr are not assigned
> @@ -2030,6 +2208,10 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>   		return -EINVAL;
>   	}
>   
> +	/* tdx_hardware_disable() uses associated_tdvcpus. */
> +	for_each_possible_cpu(i)
> +		INIT_LIST_HEAD(&per_cpu(associated_tdvcpus, i));
> +
>   	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
>   		/*
>   		 * Here it checks if MSRs (tdx_uret_msrs) can be saved/restored
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 0d8a98feb58e..7f8c78f06508 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -73,6 +73,8 @@ struct vcpu_tdx {
>   	unsigned long *tdvpx_pa;
>   	bool td_vcpu_created;
>   
> +	struct list_head cpu_list;
> +
>   	union tdx_exit_reason exit_reason;
>   
>   	bool initialized;
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 9fd997c79c33..5853f29f0af3 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -137,6 +137,7 @@ void vmx_setup_mce(struct kvm_vcpu *vcpu);
>   #ifdef CONFIG_INTEL_TDX_HOST
>   int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
>   void tdx_hardware_unsetup(void);
> +void tdx_hardware_disable(void);
>   bool tdx_is_vm_type_supported(unsigned long type);
>   int tdx_offline_cpu(void);
>   
> @@ -153,6 +154,7 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
>   fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu);
>   void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
>   void tdx_vcpu_put(struct kvm_vcpu *vcpu);
> +void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
>   u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
>   
>   int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
> @@ -171,6 +173,7 @@ void tdx_post_memory_mapping(struct kvm_vcpu *vcpu,
>   #else
>   static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return -EOPNOTSUPP; }
>   static inline void tdx_hardware_unsetup(void) {}
> +static inline void tdx_hardware_disable(void) {}
>   static inline bool tdx_is_vm_type_supported(unsigned long type) { return false; }
>   static inline int tdx_offline_cpu(void) { return 0; }
>   
> @@ -190,6 +193,7 @@ static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
>   static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) { return EXIT_FASTPATH_NONE; }
>   static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {}
>   static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {}
> +static inline void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) {}
>   static inline u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) { return 0; }
>   
>   static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }

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