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References: <cover.1664530907.git.isaku.yamahata@intel.com> <07bf749357bbf1acd20b09d7ab1fac940082632c.1664530907.git.isaku.yamahata@intel.com>
In-Reply-To: <07bf749357bbf1acd20b09d7ab1fac940082632c.1664530907.git.isaku.yamahata@intel.com>
From:   Sagi Shahar <sagis@google.com>
Date:   Wed, 12 Oct 2022 15:30:26 -0700
Message-ID: <CAAhR5DFrwP+5K8MOxz5YK7jYShhaK4A+2h1Pi31U_9+Z+cz-0A@mail.gmail.com>
Subject: Re: [PATCH v9 016/105] KVM: TDX: create/destroy VM structure
To:     isaku.yamahata@intel.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        isaku.yamahata@gmail.com, Paolo Bonzini <pbonzini@redhat.com>,
        erdemaktas@google.com, Sean Christopherson <seanjc@google.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Kai Huang <kai.huang@intel.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Sep 30, 2022 at 3:19 AM <isaku.yamahata@intel.com> wrote:
>
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> As the first step to create TDX guest, create/destroy VM struct.  Assign
> TDX private Host Key ID (HKID) to the TDX guest for memory encryption and
> allocate extra pages for the TDX guest. On destruction, free allocated
> pages, and HKID.
>
> Before tearing down private page tables, TDX requires some resources of the
> guest TD to be destroyed (i.e. keyID must have been reclaimed, etc).  Add
> flush_shadow_all_private callback before tearing down private page tables
> for it.
>
> Add a second kvm_x86_ops hook in kvm_arch_destroy_vm() to support TDX's
> destruction path, which needs to first put the VM into a teardown state,
> then free per-vCPU resources, and finally free per-VM resources.
>
> Co-developed-by: Kai Huang <kai.huang@intel.com>
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>  arch/x86/include/asm/kvm-x86-ops.h |   2 +
>  arch/x86/include/asm/kvm_host.h    |   2 +
>  arch/x86/kvm/vmx/main.c            |  34 ++-
>  arch/x86/kvm/vmx/tdx.c             | 409 +++++++++++++++++++++++++++++
>  arch/x86/kvm/vmx/tdx.h             |   2 +
>  arch/x86/kvm/vmx/x86_ops.h         |  11 +
>  arch/x86/kvm/x86.c                 |   8 +
>  7 files changed, 465 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 3857bff6949c..968e5ba1e4e6 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -21,7 +21,9 @@ KVM_X86_OP(has_emulated_msr)
>  KVM_X86_OP(vcpu_after_set_cpuid)
>  KVM_X86_OP(is_vm_type_supported)
>  KVM_X86_OP(vm_init)
> +KVM_X86_OP_OPTIONAL(flush_shadow_all_private)
>  KVM_X86_OP_OPTIONAL(vm_destroy)
> +KVM_X86_OP_OPTIONAL(vm_free)
>  KVM_X86_OP_OPTIONAL_RET0(vcpu_precreate)
>  KVM_X86_OP(vcpu_create)
>  KVM_X86_OP(vcpu_free)
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e9f4bff8e3a9..f3d16e5730ac 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1466,7 +1466,9 @@ struct kvm_x86_ops {
>         bool (*is_vm_type_supported)(unsigned long vm_type);
>         unsigned int vm_size;
>         int (*vm_init)(struct kvm *kvm);
> +       void (*flush_shadow_all_private)(struct kvm *kvm);
>         void (*vm_destroy)(struct kvm *kvm);
> +       void (*vm_free)(struct kvm *kvm);
>
>         /* Create, but do not attach this VCPU */
>         int (*vcpu_precreate)(struct kvm *kvm);
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 477c14b64879..408afa691bad 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -29,18 +29,44 @@ static __init int vt_hardware_setup(void)
>         return 0;
>  }
>
> +static void vt_hardware_unsetup(void)
> +{
> +       tdx_hardware_unsetup();
> +       vmx_hardware_unsetup();
> +}
> +
>  static int vt_vm_init(struct kvm *kvm)
>  {
>         if (is_td(kvm))
> -               return -EOPNOTSUPP;     /* Not ready to create guest TD yet. */
> +               return tdx_vm_init(kvm);
>
>         return vmx_vm_init(kvm);
>  }
>
> +static void vt_flush_shadow_all_private(struct kvm *kvm)
> +{
> +       if (is_td(kvm))
> +               return tdx_mmu_release_hkid(kvm);
> +}
> +
> +static void vt_vm_destroy(struct kvm *kvm)
> +{
> +       if (is_td(kvm))
> +               return;
> +
> +       vmx_vm_destroy(kvm);
> +}
> +
> +static void vt_vm_free(struct kvm *kvm)
> +{
> +       if (is_td(kvm))
> +               return tdx_vm_free(kvm);
> +}
> +
>  struct kvm_x86_ops vt_x86_ops __initdata = {
>         .name = "kvm_intel",
>
> -       .hardware_unsetup = vmx_hardware_unsetup,
> +       .hardware_unsetup = vt_hardware_unsetup,
>         .check_processor_compatibility = vmx_check_processor_compatibility,
>
>         .hardware_enable = vmx_hardware_enable,
> @@ -50,7 +76,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>         .is_vm_type_supported = vt_is_vm_type_supported,
>         .vm_size = sizeof(struct kvm_vmx),
>         .vm_init = vt_vm_init,
> -       .vm_destroy = vmx_vm_destroy,
> +       .flush_shadow_all_private = vt_flush_shadow_all_private,
> +       .vm_destroy = vt_vm_destroy,
> +       .vm_free = vt_vm_free,
>
>         .vcpu_precreate = vmx_vcpu_precreate,
>         .vcpu_create = vmx_vcpu_create,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index c4a318efbed5..93174b10e1ea 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -32,6 +32,399 @@ struct tdx_capabilities {
>  /* Capabilities of KVM + the TDX module. */
>  static struct tdx_capabilities tdx_caps;
>
> +/*
> + * Some TDX SEAMCALLs (TDH.MNG.CREATE, TDH.PHYMEM.CACHE.WB,
> + * TDH.MNG.KEY.RECLAIMID, TDH.MNG.KEY.FREEID etc) tries to acquire a global lock
> + * internally in TDX module.  If failed, TDX_OPERAND_BUSY is returned without
> + * spinning or waiting due to a constraint on execution time.  It's caller's
> + * responsibility to avoid race (or retry on TDX_OPERAND_BUSY).  Use this mutex
> + * to avoid race in TDX module because the kernel knows better about scheduling.
> + */
> +static DEFINE_MUTEX(tdx_lock);
> +static struct mutex *tdx_mng_key_config_lock;
> +
> +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);
> +}
> +
> +static inline bool is_td_created(struct kvm_tdx *kvm_tdx)
> +{
> +       return kvm_tdx->tdr.added;
> +}
> +
> +static inline void tdx_hkid_free(struct kvm_tdx *kvm_tdx)
> +{
> +       tdx_keyid_free(kvm_tdx->hkid);
> +       kvm_tdx->hkid = -1;
> +}
> +
> +static inline bool is_hkid_assigned(struct kvm_tdx *kvm_tdx)
> +{
> +       return kvm_tdx->hkid > 0;
> +}
> +
> +static void tdx_clear_page(unsigned long page)
> +{
> +       const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
> +       unsigned long i;
> +
> +       /*
> +        * Zeroing the page is only necessary for systems with MKTME-i:
> +        * when re-assign one page from old keyid to a new keyid, MOVDIR64B is
> +        * required to clear/write the page with new keyid to prevent integrity
> +        * error when read on the page with new keyid.
> +        *
> +        * The cache line could be poisoned (even without MKTME-i), clear the
> +        * poison bit.
> +        */
> +       for (i = 0; i < PAGE_SIZE; i += 64)
> +               movdir64b((void *)(page + i), zero_page);
> +       /*
> +        * MOVDIR64B store uses WC buffer.  Prevent following memory reads
> +        * from seeing potentially poisoned cache.
> +        */
> +       __mb();
> +}
> +
> +static int tdx_reclaim_page(unsigned long va, hpa_t pa, bool do_wb, u16 hkid)
> +{
> +       struct tdx_module_output out;
> +       u64 err;
> +
> +       err = tdh_phymem_page_reclaim(pa, &out);
> +       if (WARN_ON_ONCE(err)) {
> +               pr_tdx_error(TDH_PHYMEM_PAGE_RECLAIM, err, &out);
> +               return -EIO;
> +       }
> +
> +       if (do_wb) {
> +               err = tdh_phymem_page_wbinvd(set_hkid_to_hpa(pa, hkid));
> +               if (WARN_ON_ONCE(err)) {
> +                       pr_tdx_error(TDH_PHYMEM_PAGE_WBINVD, err, NULL);
> +                       return -EIO;
> +               }
> +       }
> +
> +       tdx_clear_page(va);
> +       return 0;
> +}
> +
> +static int tdx_alloc_td_page(struct tdx_td_page *page)
> +{
> +       page->va = __get_free_page(GFP_KERNEL_ACCOUNT);
> +       if (!page->va)
> +               return -ENOMEM;
> +
> +       page->pa = __pa(page->va);
> +       return 0;
> +}
> +
> +static inline void tdx_mark_td_page_added(struct tdx_td_page *page)
> +{
> +       WARN_ON_ONCE(page->added);
> +       page->added = true;
> +}
> +
> +static void tdx_reclaim_td_page(struct tdx_td_page *page)
> +{
> +       if (page->added) {
> +               /*
> +                * TDCX are being reclaimed.  TDX module maps TDCX with HKID
> +                * assigned to the TD.  Here the cache associated to the TD
> +                * was already flushed by TDH.PHYMEM.CACHE.WB before here, So
> +                * cache doesn't need to be flushed again.
> +                */
> +               if (tdx_reclaim_page(page->va, page->pa, false, 0))
> +                       return;
> +
> +               page->added = false;
> +       }
> +       if (page->va) {
> +               free_page(page->va);
> +               page->va = 0;
> +       }
> +}
> +
> +static int tdx_do_tdh_phymem_cache_wb(void *param)
> +{
> +       u64 err = 0;
> +
> +       do {
> +               err = tdh_phymem_cache_wb(!!err);
> +       } while (err == TDX_INTERRUPTED_RESUMABLE);
> +
> +       /* Other thread may have done for us. */
> +       if (err == TDX_NO_HKID_READY_TO_WBCACHE)
> +               err = TDX_SUCCESS;
> +       if (WARN_ON_ONCE(err)) {
> +               pr_tdx_error(TDH_PHYMEM_CACHE_WB, err, NULL);
> +               return -EIO;
> +       }
> +
> +       return 0;
> +}
> +
> +void tdx_mmu_release_hkid(struct kvm *kvm)
> +{
> +       struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> +       cpumask_var_t packages;
> +       bool cpumask_allocated;
> +       u64 err;
> +       int ret;
> +       int i;
> +
> +       if (!is_hkid_assigned(kvm_tdx))
> +               return;
> +
> +       if (!is_td_created(kvm_tdx))
> +               goto free_hkid;
> +
> +       cpumask_allocated = zalloc_cpumask_var(&packages, GFP_KERNEL);
> +       cpus_read_lock();
> +       for_each_online_cpu(i) {
> +               if (cpumask_allocated &&
> +                       cpumask_test_and_set_cpu(topology_physical_package_id(i),
> +                                               packages))
> +                       continue;
> +
> +               /*
> +                * We can destroy multiple the guest TDs simultaneously.
> +                * Prevent tdh_phymem_cache_wb from returning TDX_BUSY by
> +                * serialization.
> +                */
> +               mutex_lock(&tdx_lock);
> +               ret = smp_call_on_cpu(i, tdx_do_tdh_phymem_cache_wb, NULL, 1);
> +               mutex_unlock(&tdx_lock);
> +               if (ret)
> +                       break;
> +       }
> +       cpus_read_unlock();
> +       free_cpumask_var(packages);
> +
> +       mutex_lock(&tdx_lock);
> +       err = tdh_mng_key_freeid(kvm_tdx->tdr.pa);
> +       mutex_unlock(&tdx_lock);
> +       if (WARN_ON_ONCE(err)) {
> +               pr_tdx_error(TDH_MNG_KEY_FREEID, err, NULL);
> +               pr_err("tdh_mng_key_freeid failed. HKID %d is leaked.\n",
> +                       kvm_tdx->hkid);
> +               return;
> +       }
> +
> +free_hkid:
> +       tdx_hkid_free(kvm_tdx);
> +}
> +
> +void tdx_vm_free(struct kvm *kvm)
> +{
> +       struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> +       int i;
> +
> +       /* Can't reclaim or free TD pages if teardown failed. */
> +       if (is_hkid_assigned(kvm_tdx))
> +               return;
> +
> +       if (kvm_tdx->tdcs) {
> +               for (i = 0; i < tdx_caps.tdcs_nr_pages; i++)
> +                       tdx_reclaim_td_page(&kvm_tdx->tdcs[i]);
> +               kfree(kvm_tdx->tdcs);
> +       }
> +
> +       /*
> +        * TDX module maps TDR with TDX global HKID.  TDX module may access TDR
> +        * while operating on TD (Especially reclaiming TDCS).  Cache flush with
> +        * TDX global HKID is needed.
> +        */
> +       if (kvm_tdx->tdr.added &&
> +               tdx_reclaim_page(kvm_tdx->tdr.va, kvm_tdx->tdr.pa, true,
> +                               tdx_global_keyid))
> +               return;
> +
> +       free_page(kvm_tdx->tdr.va);
> +}
> +
> +static int tdx_do_tdh_mng_key_config(void *param)
> +{
> +       hpa_t *tdr_p = param;
> +       u64 err;
> +
> +       do {
> +               err = tdh_mng_key_config(*tdr_p);
> +
> +               /*
> +                * If it failed to generate a random key, retry it because this
> +                * is typically caused by an entropy error of the CPU's random
> +                * number generator.
> +                */
> +       } while (err == TDX_KEY_GENERATION_FAILED);
> +
> +       if (WARN_ON_ONCE(err)) {
> +               pr_tdx_error(TDH_MNG_KEY_CONFIG, err, NULL);
> +               return -EIO;
> +       }
> +
> +       return 0;
> +}
> +
> +int tdx_vm_init(struct kvm *kvm)
> +{
> +       struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> +       cpumask_var_t packages;
> +       int ret, i;
> +       u64 err;
> +
> +       /* vCPUs can't be created until after KVM_TDX_INIT_VM. */
> +       kvm->max_vcpus = 0;

The fact that vCPUs can't be created until KVM_TDX_INIT_VM is called
will make it difficult to implement intra host migration. See longer
discussion below.

> +
> +       kvm_tdx->hkid = tdx_keyid_alloc();
> +       if (kvm_tdx->hkid < 0)
> +               return -EBUSY;
> +
> +       ret = tdx_alloc_td_page(&kvm_tdx->tdr);
> +       if (ret)
> +               goto free_hkid;
> +
> +       kvm_tdx->tdcs = kcalloc(tdx_caps.tdcs_nr_pages, sizeof(*kvm_tdx->tdcs),
> +                               GFP_KERNEL_ACCOUNT | __GFP_ZERO);
> +       if (!kvm_tdx->tdcs)
> +               goto free_tdr;
> +       for (i = 0; i < tdx_caps.tdcs_nr_pages; i++) {
> +               ret = tdx_alloc_td_page(&kvm_tdx->tdcs[i]);
> +               if (ret)
> +                       goto free_tdcs;
> +       }
> +
> +       /*
> +        * Acquire global lock to avoid TDX_OPERAND_BUSY:
> +        * TDH.MNG.CREATE and other APIs try to lock the global Key Owner
> +        * Table (KOT) to track the assigned TDX private HKID.  It doesn't spin
> +        * to acquire the lock, returns TDX_OPERAND_BUSY instead, and let the
> +        * caller to handle the contention.  This is because of time limitation
> +        * usable inside the TDX module and OS/VMM knows better about process
> +        * scheduling.
> +        *
> +        * APIs to acquire the lock of KOT:
> +        * TDH.MNG.CREATE, TDH.MNG.KEY.FREEID, TDH.MNG.VPFLUSHDONE, and
> +        * TDH.PHYMEM.CACHE.WB.
> +        */
> +       mutex_lock(&tdx_lock);
> +       err = tdh_mng_create(kvm_tdx->tdr.pa, kvm_tdx->hkid);
> +       mutex_unlock(&tdx_lock);
> +       if (WARN_ON_ONCE(err)) {
> +               pr_tdx_error(TDH_MNG_CREATE, err, NULL);
> +               ret = -EIO;
> +               goto free_tdcs;
> +       }
> +       tdx_mark_td_page_added(&kvm_tdx->tdr);
> +
> +       if (!zalloc_cpumask_var(&packages, GFP_KERNEL)) {
> +               ret = -ENOMEM;
> +               goto key_freeid;
> +       }
> +       cpus_read_lock();
> +       /*
> +        * Need at least one CPU of the package to be online in order to
> +        * program all packages for host key id.  Check it.
> +        */
> +       for_each_present_cpu(i)
> +               cpumask_set_cpu(topology_physical_package_id(i), packages);
> +       for_each_online_cpu(i)
> +               cpumask_clear_cpu(topology_physical_package_id(i), packages);
> +       if (!cpumask_empty(packages)) {
> +               ret = -EIO;
> +               /*
> +                * Because it's hard for human operator to figure out the
> +                * reason, warn it.
> +                */
> +               pr_warn("All packages need to have online CPU to create TD. Online CPU and retry.\n");
> +               cpus_read_unlock();
> +               free_cpumask_var(packages);
> +               goto key_freeid;
> +       }
> +       for_each_online_cpu(i) {
> +               int pkg = topology_physical_package_id(i);
> +
> +               if (cpumask_test_and_set_cpu(pkg, packages))
> +                       continue;
> +
> +               /*
> +                * Program the memory controller in the package with an
> +                * encryption key associated to a TDX private host key id
> +                * assigned to this TDR.  Concurrent operations on same memory
> +                * controller results in TDX_OPERAND_BUSY.  Avoid this race by
> +                * mutex.
> +                */
> +               mutex_lock(&tdx_mng_key_config_lock[pkg]);
> +               ret = smp_call_on_cpu(i, tdx_do_tdh_mng_key_config,
> +                                     &kvm_tdx->tdr.pa, true);
> +               mutex_unlock(&tdx_mng_key_config_lock[pkg]);
> +               if (ret)
> +                       break;
> +       }
> +       cpus_read_unlock();
> +       free_cpumask_var(packages);
> +       if (ret)
> +               goto teardown;
> +
> +       for (i = 0; i < tdx_caps.tdcs_nr_pages; i++) {
> +               err = tdh_mng_addcx(kvm_tdx->tdr.pa, kvm_tdx->tdcs[i].pa);
> +               if (WARN_ON_ONCE(err)) {
> +                       pr_tdx_error(TDH_MNG_ADDCX, err, NULL);
> +                       ret = -EIO;
> +                       goto teardown;
> +               }
> +               tdx_mark_td_page_added(&kvm_tdx->tdcs[i]);
> +       }
> +
> +       /*
> +        * Note, TDH_MNG_INIT cannot be invoked here.  TDH_MNG_INIT requires a dedicated
> +        * ioctl() to define the configure CPUID values for the TD.
> +        */
> +       return 0;
> +
> +       /*
> +        * The sequence for freeing resources from a partially initialized TD
> +        * varies based on where in the initialization flow failure occurred.
> +        * Simply use the full teardown and destroy, which naturally play nice
> +        * with partial initialization.
> +        */
> +teardown:
> +       tdx_mmu_release_hkid(kvm);
> +       tdx_vm_free(kvm);
> +       return ret;
> +
> +key_freeid:
> +       mutex_lock(&tdx_lock);
> +       err = tdh_mng_key_freeid(kvm_tdx->tdr.pa);
> +       mutex_unlock(&tdx_lock);
> +       if (WARN_ON_ONCE(err)) {
> +               pr_tdx_error(TDH_MNG_KEY_FREEID, err, NULL);
> +               pr_err("tdh_mng_key_freeid failed. HKID %d is leaked.\n",
> +                      kvm_tdx->hkid);
> +               kvm_tdx->hkid = -1;
> +       }
> +free_tdcs:
> +       for (i = 0; i < tdx_caps.tdcs_nr_pages; i++) {
> +               if (!kvm_tdx->tdcs[i].va)
> +                       continue;
> +               free_page(kvm_tdx->tdcs[i].va);
> +       }
> +       kfree(kvm_tdx->tdcs);
> +       kvm_tdx->tdcs = NULL;
> +free_tdr:
> +       if (kvm_tdx->tdr.va) {
> +               free_page(kvm_tdx->tdr.va);
> +               kvm_tdx->tdr.added = false;
> +               kvm_tdx->tdr.va = 0;
> +               kvm_tdx->tdr.pa = 0;
> +       }
> +free_hkid:
> +       if (kvm_tdx->hkid != -1)
> +               tdx_hkid_free(kvm_tdx);
> +       return ret;
> +}
> +
>  static int __init tdx_module_setup(void)
>  {
>         const struct tdsysinfo_struct *tdsysinfo;
> @@ -82,6 +475,8 @@ bool tdx_is_vm_type_supported(unsigned long type)
>
>  int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>  {
> +       int max_pkgs;
> +       int i;
>         int r;
>
>         if (!enable_ept) {
> @@ -95,6 +490,14 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>                 return -ENODEV;
>         }
>
> +       max_pkgs = topology_max_packages();
> +       tdx_mng_key_config_lock = kcalloc(max_pkgs, sizeof(*tdx_mng_key_config_lock),
> +                                  GFP_KERNEL);
> +       if (!tdx_mng_key_config_lock)
> +               return -ENOMEM;
> +       for (i = 0; i < max_pkgs; i++)
> +               mutex_init(&tdx_mng_key_config_lock[i]);
> +
>         /* TDX requires VMX. */
>         r = vmxon_all();
>         if (!r)
> @@ -103,3 +506,9 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
>
>         return r;
>  }
> +
> +void tdx_hardware_unsetup(void)
> +{
> +       /* kfree accepts NULL. */
> +       kfree(tdx_mng_key_config_lock);
> +}
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 98999bf3f188..938314635b47 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -17,6 +17,8 @@ struct kvm_tdx {
>
>         struct tdx_td_page tdr;
>         struct tdx_td_page *tdcs;
> +
> +       int hkid;
>  };
>
>  struct vcpu_tdx {
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 2a870202fbf6..ce50ddef84bf 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -133,9 +133,20 @@ void vmx_setup_mce(struct kvm_vcpu *vcpu);
>  #ifdef CONFIG_INTEL_TDX_HOST
>  int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops);
>  bool tdx_is_vm_type_supported(unsigned long type);
> +void tdx_hardware_unsetup(void);
> +
> +int tdx_vm_init(struct kvm *kvm);
> +void tdx_mmu_release_hkid(struct kvm *kvm);
> +void tdx_vm_free(struct kvm *kvm);
>  #else
>  static inline int tdx_hardware_setup(struct kvm_x86_ops *x86_ops) { return 0; }
>  static inline bool tdx_is_vm_type_supported(unsigned long type) { return false; }
> +static inline void tdx_hardware_unsetup(void) {}
> +
> +static inline int tdx_vm_init(struct kvm *kvm) { return -EOPNOTSUPP; }
> +static inline void tdx_mmu_release_hkid(struct kvm *kvm) {}
> +static inline void tdx_flush_shadow_all_private(struct kvm *kvm) {}
> +static inline void tdx_vm_free(struct kvm *kvm) {}
>  #endif
>
>  #endif /* __KVM_X86_VMX_X86_OPS_H */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1df0dac476bc..82e6f54b35fb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12426,6 +12426,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>         kvm_page_track_cleanup(kvm);
>         kvm_xen_destroy_vm(kvm);
>         kvm_hv_destroy_vm(kvm);
> +       static_call_cond(kvm_x86_vm_free)(kvm);
>  }
>
>  static void memslot_rmap_free(struct kvm_memory_slot *slot)
> @@ -12736,6 +12737,13 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>
>  void kvm_arch_flush_shadow_all(struct kvm *kvm)
>  {
> +       /*
> +        * kvm_mmu_zap_all() zaps both private and shared page tables.  Before
> +        * tearing down private page tables, TDX requires some TD resources to
> +        * be destroyed (i.e. keyID must have been reclaimed, etc).  Invoke
> +        * kvm_x86_flush_shadow_all_private() for this.
> +        */
> +       static_call_cond(kvm_x86_flush_shadow_all_private)(kvm);
>         kvm_mmu_zap_all(kvm);
>  }
>
> --
> 2.25.1
>

Me, Sean and Isaku had a short discussion offline regarding the
interaction between the proposed API in this patch and intra-host
migration. To summarize:

For intra-host migration you generally want the destination VM to be
initialized including the right number of vCPUs before you migrate the
source VM state into it.
The proposed API makes it difficult since it forces the destination VM
to call KVM_TDX_INIT_VM before creating vCPUs which initializes TDX
state and allocate a new hkid for the destination VM which would never
be used. This can create a resource limitation on migrating VMs where
there shouldn't be one.

To solve this issue there are 2 main proposed changes to the API:

1. Add a new API based on ioctl(KVM_ENABLE_CAP) to let userspace
modify the max number of vcpus:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 43a6a7efc6ec..6055098b025b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6278,6 +6278,18 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
                }
                mutex_unlock(&kvm->lock);
                break;
+       case KVM_CAP_MAX_VCPUS:
+               r = -EINVAL;
+               if (cap->args[0] > KVM_MAX_VCPUS)
+                       break;
+
+               mutex_lock(&kvm->lock);
+               if (!kvm->created_vcpus) {
+                       kvm->max_vcpus = cap->args[0];
+                       r = 0;
+               }
+               mutex_unlock(&kvm->lock);
+               break;
        case KVM_CAP_MAX_VCPU_ID:
                r = -EINVAL;
                if (cap->args[0] > KVM_MAX_VCPU_IDS)

2. Modify the existing API such that max_vcpus will be set to
KVM_MAX_VCPUS like in regular VMs and during KVM_TDX_INIT_VM, if the
user created more vCPUs than the number specified, KVM_TDX_INIT_VM
will fail.

For option (1), there are some possible variations:
1.a. Do we keep the max_vcpus argument in KVM_TDX_INIT_VM? If so, we
need to check if max_vcpus matches the number of max_vcpus already set
and fail otherwise.
1.b. Do we require KVM_ENABLE_CAP_VM(KVM_CAP_MAX_VCPUS) to be called?
Theoretically, we can set max_vcpus to the KVM default KVM_MAX_VCPUS
and allow the user to change it as long as vcpus hasn't been created.
If KVM_ENABLE_CAP_VM(KVM_CAP_MAX_VCPUS), the behavior will remain the
same as regular VMs right now.

In my opinion, the cleanest solution would be option 1 (new
KVM_CAP_MAX_VCPUS API) while removing the max_vcpus argument from
KVM_TDX_INIT_VM and setting the initial max_vcpus to KVM_MAX_VCPUS and
not requiring the new ioctl to be called unless userspace wants to
specifically limit the number of vcpus. In that case,
KVM_CAP_MAX_VCPUS can be called at any time until vcpus are created.