Re: [PATCH v19 044/130] KVM: TDX: Do TDX specific vcpu initialization

Isaku Yamahata
2024-03-21T20:43:46Z

On Thu, Mar 21, 2024 at 01:43:14PM +0800,
Chao Gao <chao.gao@intel.com> wrote:

> >+/* VMM can pass one 64bit auxiliary data to vcpu via RCX for guest BIOS. */
> >+static int tdx_td_vcpu_init(struct kvm_vcpu *vcpu, u64 vcpu_rcx)
> >+{
> >+ struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> >+ struct vcpu_tdx *tdx = to_tdx(vcpu);
> >+ unsigned long *tdvpx_pa = NULL;
> >+ unsigned long tdvpr_pa;
> >+ unsigned long va;
> >+ int ret, i;
> >+ u64 err;
> >+
> >+ if (is_td_vcpu_created(tdx))
> >+ return -EINVAL;
> >+
> >+ /*
> >+ * vcpu_free method frees allocated pages. Avoid partial setup so
> >+ * that the method can't handle it.
> >+ */
> >+ va = __get_free_page(GFP_KERNEL_ACCOUNT);
> >+ if (!va)
> >+ return -ENOMEM;
> >+ tdvpr_pa = __pa(va);
> >+
> >+ tdvpx_pa = kcalloc(tdx_info->nr_tdvpx_pages, sizeof(*tdx->tdvpx_pa),
> >+ GFP_KERNEL_ACCOUNT);
> >+ if (!tdvpx_pa) {
> >+ ret = -ENOMEM;
> >+ goto free_tdvpr;
> >+ }
> >+ for (i = 0; i < tdx_info->nr_tdvpx_pages; i++) {
> >+ va = __get_free_page(GFP_KERNEL_ACCOUNT);
> >+ if (!va) {
> >+ ret = -ENOMEM;
> >+ goto free_tdvpx;
> >+ }
> >+ tdvpx_pa[i] = __pa(va);
> >+ }
> >+
> >+ err = tdh_vp_create(kvm_tdx->tdr_pa, tdvpr_pa);
> >+ if (KVM_BUG_ON(err, vcpu->kvm)) {
> >+ ret = -EIO;
> >+ pr_tdx_error(TDH_VP_CREATE, err, NULL);
> >+ goto free_tdvpx;
> >+ }
> >+ tdx->tdvpr_pa = tdvpr_pa;
> >+
> >+ tdx->tdvpx_pa = tdvpx_pa;
> >+ for (i = 0; i < tdx_info->nr_tdvpx_pages; i++) {
>
> Can you merge the for-loop above into this one? then ...
>
> >+ err = tdh_vp_addcx(tdx->tdvpr_pa, tdvpx_pa[i]);
> >+ if (KVM_BUG_ON(err, vcpu->kvm)) {
> >+ pr_tdx_error(TDH_VP_ADDCX, err, NULL);
>
> >+ for (; i < tdx_info->nr_tdvpx_pages; i++) {
> >+ free_page((unsigned long)__va(tdvpx_pa[i]));
> >+ tdvpx_pa[i] = 0;
> >+ }
>
> ... no need to free remaining pages.

Makes sense. Let me clean up this.

> >+ /* vcpu_free method frees TDVPX and TDR donated to TDX */
> >+ return -EIO;
> >+ }
> >+ }
> >+
> >+ err = tdh_vp_init(tdx->tdvpr_pa, vcpu_rcx);
> >+ if (KVM_BUG_ON(err, vcpu->kvm)) {
> >+ pr_tdx_error(TDH_VP_INIT, err, NULL);
> >+ return -EIO;
> >+ }
> >+
> >+ vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
> >+ tdx->td_vcpu_created = true;
> >+ return 0;
> >+
> >+free_tdvpx:
> >+ for (i = 0; i < tdx_info->nr_tdvpx_pages; i++) {
> >+ if (tdvpx_pa[i])
> >+ free_page((unsigned long)__va(tdvpx_pa[i]));
> >+ tdvpx_pa[i] = 0;
> >+ }
> >+ kfree(tdvpx_pa);
> >+ tdx->tdvpx_pa = NULL;
> >+free_tdvpr:
> >+ if (tdvpr_pa)
> >+ free_page((unsigned long)__va(tdvpr_pa));
> >+ tdx->tdvpr_pa = 0;
> >+
> >+ return ret;
> >+}
> >+
> >+int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
> >+{
> >+ struct msr_data apic_base_msr;
> >+ struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> >+ struct vcpu_tdx *tdx = to_tdx(vcpu);
> >+ struct kvm_tdx_cmd cmd;
> >+ int ret;
> >+
> >+ if (tdx->initialized)
> >+ return -EINVAL;
> >+
> >+ if (!is_hkid_assigned(kvm_tdx) || is_td_finalized(kvm_tdx))
>
> These checks look random e.g., I am not sure why is_td_created() isn't check here.
>
> A few helper functions and boolean variables are added to track which stage the
> TD or TD vCPU is in. e.g.,
>
> is_hkid_assigned()
> is_td_finalized()
> is_td_created()
> tdx->initialized
> td_vcpu_created
>
> Insteading of doing this, I am wondering if adding two state machines for
> TD and TD vCPU would make the implementation clear and easy to extend.

Let me look into the state machine. Originally I hoped we don't need it, but
it seems to deserve the state machine..

> >+ return -EINVAL;
> >+
> >+ if (copy_from_user(&cmd, argp, sizeof(cmd)))
> >+ return -EFAULT;
> >+
> >+ if (cmd.error)
> >+ return -EINVAL;
> >+
> >+ /* Currently only KVM_TDX_INTI_VCPU is defined for vcpu operation. */
> >+ if (cmd.flags || cmd.id != KVM_TDX_INIT_VCPU)
> >+ return -EINVAL;
>
> Even though KVM_TD_INIT_VCPU is the only supported command, it is worthwhile to
> use a switch-case statement. New commands can be added easily without the need
> to refactor this function first.

Yes. For KVM_MAP_MEMORY, I will make KVM_TDX_INIT_MEM_REGION vcpu ioctl instead
of vm ioctl because it is consistent and scalable. We'll have switch statement
in the next respin.

> >+
> >+ /*
> >+ * As TDX requires X2APIC, set local apic mode to X2APIC. User space
> >+ * VMM, e.g. qemu, is required to set CPUID[0x1].ecx.X2APIC=1 by
> >+ * KVM_SET_CPUID2. Otherwise kvm_set_apic_base() will fail.
> >+ */
> >+ apic_base_msr = (struct msr_data) {
> >+ .host_initiated = true,
> >+ .data = APIC_DEFAULT_PHYS_BASE | LAPIC_MODE_X2APIC |
> >+ (kvm_vcpu_is_reset_bsp(vcpu) ? MSR_IA32_APICBASE_BSP : 0),
> >+ };
> >+ if (kvm_set_apic_base(vcpu, &apic_base_msr))
> >+ return -EINVAL;
>
> Exporting kvm_vcpu_is_reset_bsp() and kvm_set_apic_base() should be done
> here (rather than in a previous patch).

Sure.

> >+
> >+ ret = tdx_td_vcpu_init(vcpu, (u64)cmd.data);
> >+ if (ret)
> >+ return ret;
> >+
> >+ tdx->initialized = true;
> >+ return 0;
> >+}
> >+
>
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index c002761bb662..2bd4b7c8fa51 100644
> >--- a/arch/x86/kvm/x86.c
> >+++ b/arch/x86/kvm/x86.c
> >@@ -6274,6 +6274,12 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> > case KVM_SET_DEVICE_ATTR:
> > r = kvm_vcpu_ioctl_device_attr(vcpu, ioctl, argp);
> > break;
> >+ case KVM_MEMORY_ENCRYPT_OP:
> >+ r = -ENOTTY;
>
> Maybe -EINVAL is better. Because previously trying to call this on vCPU fd
> failed with -EINVAL given ...

Oh, ok. Will change it. I followed VM ioctl case as default value. But vcpu
ioctl seems to have -EINVAL as default value.
--
Isaku Yamahata <isaku.yamahata@intel.com>