linux-kernel - Re: [PATCH v3 22/24] x86/tdx: Add/Remove DPAMT pages for guest private memory to demote

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Message-ID: <2b9d6a33629b40c92ecf1d9ed5d75e2158528721.camel@intel.com>
Date: Mon, 19 Jan 2026 10:52:46 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
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	"Li, Xiaoyao" <xiaoyao.li@...el.com>, "Gao, Chao" <chao.gao@...el.com>,
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 Chao P" <chao.p.peng@...el.com>, "francescolavra.fl@...il.com"
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Subject: Re: [PATCH v3 22/24] x86/tdx: Add/Remove DPAMT pages for guest
 private memory to demote

On Tue, 2026-01-06 at 18:24 +0800, Yan Zhao wrote:
>  u64 tdh_mem_page_demote(struct tdx_td *td, u64 gpa, int level, struct page *new_sept_page,
> +			struct tdx_prealloc *prealloc,
>  			u64 *ext_err1, u64 *ext_err2)
>  {
> -	struct tdx_module_args args = {
> -		.rcx = gpa | level,
> -		.rdx = tdx_tdr_pa(td),
> -		.r8 = page_to_phys(new_sept_page),
> +	bool dpamt = tdx_supports_dynamic_pamt(&tdx_sysinfo) && level == TDX_PS_2M;

The spec of TDH.MEM.PAGE.DEMOTE says:

  If the TDX Module is configured to use Dynamic PAMT and the large page
  level is 1 (2MB), R12 contains the host physical address of a new 
  PAMT page (HKID bits must be 0).

It says "... is configured to use Dynamic PAMT ...", but not ".. Dynamic
PAMT is supported ..".

tdx_supports_dynamic_pamt() only reports whether the module "supports"
DPAMT.  Although in the DPAMT series the kernel always enables DPAMT when
it is supported, I think it's better to have a comment point out this fact
so we don't need to go to that series to figure out.

> +	u64 guest_memory_pamt_page[MAX_TDX_ARG_SIZE(r12)];
> +	struct tdx_module_array_args args = {
> +		.args.rcx = gpa | level,
> +		.args.rdx = tdx_tdr_pa(td),
> +		.args.r8 = page_to_phys(new_sept_page),
>  	};
>  	u64 ret;
>  
>  	if (!tdx_supports_demote_nointerrupt(&tdx_sysinfo))
>  		return TDX_SW_ERROR;
>  
> +	if (dpamt) {
> +		u64 *args_array = dpamt_args_array_ptr_r12(&args);
> +
> +		if (alloc_pamt_array(guest_memory_pamt_page, prealloc))
> +			return TDX_SW_ERROR;
> +
> +		/*
> +		 * Copy PAMT page PAs of the guest memory into the struct per the
> +		 * TDX ABI
> +		 */
> +		memcpy(args_array, guest_memory_pamt_page,
> +		       tdx_dpamt_entry_pages() * sizeof(*args_array));
> +	}