linux-kernel - Re: [PATCH v3 07/16] x86/virt/tdx: Add tdx_alloc/free

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Message-ID: <aNo7tGlyGhVdGze9@yzhao56-desk.sh.intel.com>
Date: Mon, 29 Sep 2025 15:56:36 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
CC: <kas@...nel.org>, <bp@...en8.de>, <chao.gao@...el.com>,
	<dave.hansen@...ux.intel.com>, <isaku.yamahata@...el.com>,
	<kai.huang@...el.com>, <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <mingo@...hat.com>, <pbonzini@...hat.com>,
	<seanjc@...gle.com>, <tglx@...utronix.de>, <x86@...nel.org>,
	<vannapurve@...gle.com>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v3 07/16] x86/virt/tdx: Add tdx_alloc/free_page() helpers

> +/*
> + * The TDX spec treats the registers like an array, as they are ordered
> + * in the struct. The array size is limited by the number or registers,
> + * so define the max size it could be for worst case allocations and sanity
> + * checking.
> + */
> +#define MAX_DPAMT_ARG_SIZE (sizeof(struct tdx_module_args) - \
> +			    offsetof(struct tdx_module_args, rdx))
The rdx doesn't work for tdh_mem_page_demote(), which copies the pamt pages
array starting from r12.

Is there a way to make this more generic?

> +/*
> + * Treat struct the registers like an array that starts at RDX, per
> + * TDX spec. Do some sanitychecks, and return an indexable type.
> + */
> +static u64 *dpamt_args_array_ptr(struct tdx_module_args *args)
> +{
> +	WARN_ON_ONCE(tdx_dpamt_entry_pages() > MAX_DPAMT_ARG_SIZE);
> +
> +	/*
> +	 * FORTIFY_SOUCE could inline this and complain when callers copy
> +	 * across fields, which is exactly what this is supposed to be
> +	 * used for. Obfuscate it.
> +	 */
> +	return (u64 *)((u8 *)args + offsetof(struct tdx_module_args, rdx));
> +}
> +
> +static int alloc_pamt_array(u64 *pa_array)
> +{
> +	struct page *page;
> +
> +	for (int i = 0; i < tdx_dpamt_entry_pages(); i++) {
> +		page = alloc_page(GFP_KERNEL);
> +		if (!page)
> +			return -ENOMEM;
When the 1st alloc_page() succeeds but the 2nd alloc_page() fails, the 1st page
must be freed before returning an error. 

> +		pa_array[i] = page_to_phys(page);
> +	}
> +
> +	return 0;
> +}
> +