linux-kernel - Re: [PATCH v8 14/16] x86/virt/tdx: Initialize all TDMRs

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Date:   Fri, 6 Jan 2023 16:17:32 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     linux-mm@...ck.org, peterz@...radead.org, tglx@...utronix.de,
        seanjc@...gle.com, pbonzini@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, kirill.shutemov@...ux.intel.com,
        ying.huang@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, tony.luck@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
        sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v8 14/16] x86/virt/tdx: Initialize all TDMRs

On 12/8/22 22:52, Kai Huang wrote:
> After the global KeyID has been configured on all packages, initialize
> all TDMRs to make all TDX-usable memory regions that are passed to the
> TDX module become usable.
> 
> This is the last step of initializing the TDX module.
> 
> Initializing different TDMRs can be parallelized.  For now to keep it
> simple, just initialize all TDMRs one by one.  It can be enhanced in the
> future.

The changelog probably also needs a note about this being a long process
and also at least touching on *why* it takes so long.

> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 4c779e8412f1..8b7314f19df2 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1006,6 +1006,55 @@ static int config_global_keyid(void)
>  	return ret;
>  }
>  
> +static int init_tdmr(struct tdmr_info *tdmr)
> +{
> +	u64 next;
> +
> +	/*
> +	 * Initializing a TDMR can be time consuming.  To avoid long
> +	 * SEAMCALLs, the TDX module may only initialize a part of the
> +	 * TDMR in each call.
> +	 */
> +	do {
> +		struct tdx_module_output out;
> +		int ret;
> +
> +		/* All 0's are unused parameters, they mean nothing. */
> +		ret = seamcall(TDH_SYS_TDMR_INIT, tdmr->base, 0, 0, 0, NULL,
> +				&out);
> +		if (ret)
> +			return ret;
> +		/*
> +		 * RDX contains 'next-to-initialize' address if
> +		 * TDH.SYS.TDMR.INT succeeded.

This reads strangely.  "Success" to me really is different from "partial
success".  Sure, partial success is also not an error, *but* this can be
explained better.  How about:

		 * RDX contains 'next-to-initialize' address if
		 * TDH.SYS.TDMR.INT did not fully complete and should
		 * be retried.


> +		 */
> +		next = out.rdx;
> +		cond_resched();
> +		/* Keep making SEAMCALLs until the TDMR is done */
> +	} while (next < tdmr->base + tdmr->size);
> +
> +	return 0;
> +}
> +
> +static int init_tdmrs(struct tdmr_info_list *tdmr_list)
> +{
> +	int i;
> +
> +	/*
> +	 * This operation is costly.  It can be parallelized,
> +	 * but keep it simple for now.
> +	 */
> +	for (i = 0; i < tdmr_list->nr_tdmrs; i++) {
> +		int ret;
> +
> +		ret = init_tdmr(tdmr_entry(tdmr_list, i));
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  static int init_tdx_module(void)
>  {
>  	/*
> @@ -1076,14 +1125,10 @@ static int init_tdx_module(void)
>  	if (ret)
>  		goto out_free_pamts;
>  
> -	/*
> -	 * TODO:
> -	 *
> -	 *  - Initialize all TDMRs.
> -	 *
> -	 *  Return error before all steps are done.
> -	 */
> -	ret = -EINVAL;
> +	/* Initialize TDMRs to complete the TDX module initialization */
> +	ret = init_tdmrs(&tdmr_list);
> +	if (ret)
> +		goto out_free_pamts;
>  out_free_pamts:
>  	if (ret) {
>  		/*
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index f5c12a2543d4..163c4876dee4 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -21,6 +21,7 @@
>   */
>  #define TDH_SYS_KEY_CONFIG	31
>  #define TDH_SYS_INFO		32
> +#define TDH_SYS_TDMR_INIT	36
>  #define TDH_SYS_CONFIG		45
>  
>  struct cmr_info {