linux-kernel - Re: [PATCH 20/21] KVM: TDX: Finalize VM initialization

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Message-ID: <58a801d7-72e2-4a6d-8d0b-6d7f37adaf88@intel.com>
Date: Wed, 4 Sep 2024 18:37:37 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>, seanjc@...gle.com,
 pbonzini@...hat.com, kvm@...r.kernel.org
Cc: kai.huang@...el.com, dmatlack@...gle.com, isaku.yamahata@...il.com,
 yan.y.zhao@...el.com, nik.borisov@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/21] KVM: TDX: Finalize VM initialization

On 4/09/24 06:07, Rick Edgecombe wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Add a new VM-scoped KVM_MEMORY_ENCRYPT_OP IOCTL subcommand,
> KVM_TDX_FINALIZE_VM, to perform TD Measurement Finalization.
> 
> Documentation for the API is added in another patch:
> "Documentation/virt/kvm: Document on Trust Domain Extensions(TDX)"
> 
> For the purpose of attestation, a measurement must be made of the TDX VM
> initial state. This is referred to as TD Measurement Finalization, and
> uses SEAMCALL TDH.MR.FINALIZE, after which:
> 1. The VMM adding TD private pages with arbitrary content is no longer
>    allowed
> 2. The TDX VM is runnable
> 
> Co-developed-by: Adrian Hunter <adrian.hunter@...el.com>
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
> TDX MMU part 2 v1:
>  - Added premapped check.
>  - Update for the wrapper functions for SEAMCALLs. (Sean)
>  - Add check if nr_premapped is zero.  If not, return error.
>  - Use KVM_BUG_ON() in tdx_td_finalizer() for consistency.
>  - Change tdx_td_finalizemr() to take struct kvm_tdx_cmd *cmd and return error
>    (Adrian)
>  - Handle TDX_OPERAND_BUSY case (Adrian)
>  - Updates from seamcall overhaul (Kai)
>  - Rename error->hw_error
> 
> v18:
>  - Remove the change of tools/arch/x86/include/uapi/asm/kvm.h.
> 
> v15:
>  - removed unconditional tdx_track() by tdx_flush_tlb_current() that
>    does tdx_track().
> ---
>  arch/x86/include/uapi/asm/kvm.h |  1 +
>  arch/x86/kvm/vmx/tdx.c          | 28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index 789d1d821b4f..0b4827e39458 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -932,6 +932,7 @@ enum kvm_tdx_cmd_id {
>  	KVM_TDX_INIT_VM,
>  	KVM_TDX_INIT_VCPU,
>  	KVM_TDX_INIT_MEM_REGION,
> +	KVM_TDX_FINALIZE_VM,
>  	KVM_TDX_GET_CPUID,
>  
>  	KVM_TDX_CMD_NR_MAX,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 796d1a495a66..3083a66bb895 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1257,6 +1257,31 @@ void tdx_flush_tlb_current(struct kvm_vcpu *vcpu)
>  	ept_sync_global();
>  }
>  
> +static int tdx_td_finalizemr(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
> +{
> +	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> +
> +	if (!is_hkid_assigned(kvm_tdx) || is_td_finalized(kvm_tdx))
> +		return -EINVAL;
> +	/*
> +	 * Pages are pending for KVM_TDX_INIT_MEM_REGION to issue
> +	 * TDH.MEM.PAGE.ADD().
> +	 */
> +	if (atomic64_read(&kvm_tdx->nr_premapped))
> +		return -EINVAL;
> +
> +	cmd->hw_error = tdh_mr_finalize(kvm_tdx);
> +	if ((cmd->hw_error & TDX_SEAMCALL_STATUS_MASK) == TDX_OPERAND_BUSY)
> +		return -EAGAIN;
> +	if (KVM_BUG_ON(cmd->hw_error, kvm)) {
> +		pr_tdx_error(TDH_MR_FINALIZE, cmd->hw_error);
> +		return -EIO;
> +	}
> +
> +	kvm_tdx->finalized = true;
> +	return 0;
> +}

Isaku was going to lock the mmu.  Seems like the change got lost.
To protect against racing with KVM_PRE_FAULT_MEMORY,
KVM_TDX_INIT_MEM_REGION, tdx_sept_set_private_spte() etc
e.g. Rename tdx_td_finalizemr to __tdx_td_finalizemr and add:

static int tdx_td_finalizemr(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
{
	int ret;

	write_lock(&kvm->mmu_lock);
	ret = __tdx_td_finalizemr(kvm, cmd);
	write_unlock(&kvm->mmu_lock);

	return ret;
}

> +
>  int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
>  {
>  	struct kvm_tdx_cmd tdx_cmd;
> @@ -1281,6 +1306,9 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
>  	case KVM_TDX_INIT_VM:
>  		r = tdx_td_init(kvm, &tdx_cmd);
>  		break;
> +	case KVM_TDX_FINALIZE_VM:
> +		r = tdx_td_finalizemr(kvm, &tdx_cmd);
> +		break;
>  	default:
>  		r = -EINVAL;
>  		goto out;