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Date: Tue, 22 Mar 2022 17:54:45 -0700
From: Erdem Aktas <erdemaktas@...gle.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
Cc: "open list:KERNEL VIRTUAL MACHINE (KVM)" <kvm@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>,
isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
Connor Kuehl <ckuehl@...hat.com>,
Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 073/104] KVM: TDX: track LP tdx vcpu run and
teardown vcpus on descroing the guest TD
On Fri, Mar 4, 2022 at 11:50 AM <isaku.yamahata@...el.com> wrote:
>
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> When shutting down the machine, (VMX or TDX) vcpus needs to be shutdown on
> 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 | 23 +++++++++++--
> arch/x86/kvm/vmx/tdx.c | 70 ++++++++++++++++++++++++++++++++++++--
> arch/x86/kvm/vmx/tdx.h | 2 ++
> arch/x86/kvm/vmx/x86_ops.h | 4 +++
> 4 files changed, 95 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 2cd5ba0e8788..882358ac270b 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -13,6 +13,25 @@ static bool vt_is_vm_type_supported(unsigned long type)
> return type == KVM_X86_DEFAULT_VM || tdx_is_vm_type_supported(type);
> }
>
> +static int vt_hardware_enable(void)
> +{
> + int ret;
> +
> + ret = vmx_hardware_enable();
> + if (ret)
> + return ret;
> +
> + tdx_hardware_enable();
> + return 0;
> +}
> +
> +static void vt_hardware_disable(void)
> +{
> + /* Note, TDX *and* VMX need to be disabled if TDX is enabled. */
> + tdx_hardware_disable();
> + vmx_hardware_disable();
> +}
> +
> static __init int vt_hardware_setup(void)
> {
> int ret;
> @@ -199,8 +218,8 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>
> .hardware_unsetup = vt_hardware_unsetup,
>
> - .hardware_enable = vmx_hardware_enable,
> - .hardware_disable = vmx_hardware_disable,
> + .hardware_enable = vt_hardware_enable,
> + .hardware_disable = vt_hardware_disable,
> .cpu_has_accelerated_tpr = report_flexpriority,
> .has_emulated_msr = vmx_has_emulated_msr,
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index a6b1a8ce888d..690298fb99c7 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -48,6 +48,14 @@ struct tdx_capabilities tdx_caps;
> static DEFINE_MUTEX(tdx_lock);
> static struct mutex *tdx_mng_key_config_lock;
>
> +/*
> + * A per-CPU list of TD vCPUs associated with a given CPU. Used when a CPU
> + * is brought down to invoke TDH_VP_FLUSH on the approapriate TD vCPUS.
> + * 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 u64 hkid_mask __ro_after_init;
> static u8 hkid_start_pos __ro_after_init;
>
> @@ -87,6 +95,8 @@ static inline bool is_td_finalized(struct kvm_tdx *kvm_tdx)
>
> static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
> {
> + 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
> @@ -97,6 +107,22 @@ static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
> vcpu->cpu = -1;
> }
>
> +void tdx_hardware_enable(void)
> +{
> + INIT_LIST_HEAD(&per_cpu(associated_tdvcpus, raw_smp_processor_id()));
> +}
> +
> +void tdx_hardware_disable(void)
> +{
> + int cpu = raw_smp_processor_id();
> + struct list_head *tdvcpus = &per_cpu(associated_tdvcpus, cpu);
> + struct vcpu_tdx *tdx, *tmp;
> +
> + /* Safe variant needed as tdx_disassociate_vp() deletes the entry. */
> + list_for_each_entry_safe(tdx, tmp, tdvcpus, cpu_list)
> + tdx_disassociate_vp(&tdx->vcpu);
> +}
> +
> static void tdx_clear_page(unsigned long page)
> {
> const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
> @@ -230,9 +256,11 @@ void tdx_mmu_prezap(struct kvm *kvm)
> struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> cpumask_var_t packages;
> bool cpumask_allocated;
> + struct kvm_vcpu *vcpu;
> u64 err;
> int ret;
> int i;
> + unsigned long j;
>
> if (!is_hkid_assigned(kvm_tdx))
> return;
> @@ -248,6 +276,17 @@ void tdx_mmu_prezap(struct kvm *kvm)
> return;
> }
>
> + kvm_for_each_vcpu(j, vcpu, kvm)
> + tdx_flush_vp_on_cpu(vcpu);
> +
> + mutex_lock(&tdx_lock);
> + err = tdh_mng_vpflushdone(kvm_tdx->tdr.pa);
Hi Isaku,
I am wondering about the impact of the failures on these functions. Is
there any other function which recovers any failures here?
When I look at the tdx_flush_vp function, it seems like it can fail
due to task migration so tdx_flush_vp_on_cpu might also fail and if it
fails, tdh_mng_vpflushdone returns err. Since tdx_vm_teardown does not
return any error , how the VMM can free the keyid used in this TD.
Will they be forever in "used state"?
Also if tdx_vm_teardown fails, the kvm_tdx->hkid is never set to -1
which will prevent tdx_vcpu_free to free and reclaim the resources
allocated for the vcpu.
-Erdem
> + mutex_unlock(&tdx_lock);
> + if (WARN_ON_ONCE(err)) {
> + pr_tdx_error(TDH_MNG_VPFLUSHDONE, err, NULL);
> + return;
> + }
> +
> cpumask_allocated = zalloc_cpumask_var(&packages, GFP_KERNEL);
> for_each_online_cpu(i) {
> if (cpumask_allocated &&
> @@ -472,8 +511,22 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
>
> void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> {
> - if (vcpu->cpu != cpu)
> - tdx_flush_vp_on_cpu(vcpu);
> + 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)
> @@ -522,6 +575,19 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu)
> tdx_reclaim_td_page(&tdx->tdvpx[i]);
> kfree(tdx->tdvpx);
> tdx_reclaim_td_page(&tdx->tdvpr);
> +
> + /*
> + * kvm_free_vcpus()
> + * -> kvm_unload_vcpu_mmu()
> + *
> + * does vcpu_load() for every vcpu after they already disassociated
> + * from the per cpu list when tdx_vm_teardown(). 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_flush_vp_on_cpu(vcpu);
> + WARN_ON(vcpu->cpu != -1);
> }
>
> void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 8b1cf9c158e3..180360a65545 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -81,6 +81,8 @@ struct vcpu_tdx {
> struct tdx_td_page tdvpr;
> struct tdx_td_page *tdvpx;
>
> + 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 ceafd6e18f4e..aae0f4449ec5 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -132,6 +132,8 @@ void __init tdx_pre_kvm_init(unsigned int *vcpu_size,
> bool tdx_is_vm_type_supported(unsigned long type);
> void __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
> void tdx_hardware_unsetup(void);
> +void tdx_hardware_enable(void);
> +void tdx_hardware_disable(void);
>
> int tdx_vm_init(struct kvm *kvm);
> void tdx_mmu_prezap(struct kvm *kvm);
> @@ -156,6 +158,8 @@ static inline void tdx_pre_kvm_init(
> static inline bool tdx_is_vm_type_supported(unsigned long type) { return false; }
> static inline void tdx_hardware_setup(struct kvm_x86_ops *x86_ops) {}
> static inline void tdx_hardware_unsetup(void) {}
> +static inline void tdx_hardware_enable(void) {}
> +static inline void tdx_hardware_disable(void) {}
>
> static inline int tdx_vm_init(struct kvm *kvm) { return -EOPNOTSUPP; }
> static inline void tdx_mmu_prezap(struct kvm *kvm) {}
> --
> 2.25.1
>
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