Re: [PATCH v3 6/6] x86/virt/tdx: Support DPAMT when adding memory for the extensions

[Tony Lindgren]

On Tue, Oct 06, 2026 at 01:41:50AM +0800, Xu Yilun wrote:
> The TDX module uses Physical Address Metadata Table (PAMT) to track some
> state for each page of physical memory that it might use. 3 levels of
> PAMTs are used to track pages of different sizes - 1GB, 2MB and 4KB.
> Dynamic PAMT (DPAMT) allows saving memory by allocating 4KB PAMT
> dynamically, while the 1GB and 2MB levels remain allocated on TDX module
> initialization. The kernel has helpers to install 4K DPAMT.
> 
> Although the memory for the extensions is tens of megabytes and the host
> allocates it in a large chunk, the TDX module accepts it at 4K
> granularity. Thus the host has to install 4K DPAMT for each page of it.
> 
> Call tdx_pamt_get() for each page before adding it to TDX module.
> Normally, these operations should not fail, and if they do,
> intentionally keep the error handling as simple as before - leak all
> pages, including the installed 4K DPAMT metadata.
> 
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> ---
> v3:
>  - New patch
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 5d5f9da1ab02..27a7039ee443 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1330,8 +1330,15 @@ static __init int tdx_ext_mem_setup(void)
>  		struct page *chunk = page + added_pages;
>  		unsigned int i;
>  
> -		for (i = 0; i < chunk_pages; i++)
> +		for (i = 0; i < chunk_pages; i++) {
> +			ret = tdx_pamt_get(page_to_pfn(chunk + i), NULL);
> +			if (ret) {
> +				WARN(1, "DPAMT setup error for extensions, stranded all pages\n");
> +				goto out_free_hpa_list;
> +			}
> +
>  			hpa_list->phys[i] = page_to_phys(chunk + i);
> +		}
>  
>  		ret = tdx_ext_mem_add(hpa_list, chunk_pages);
>  		if (ret) {
> 

How about just fold this change in into patch 3/6?