linux-kernel - Re: [PATCH 2/2] x86/tdx: Skip clearing reclaimed pages unless X86_BUG_TDX_PW

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Message-ID: <4bce6d90-c0d4-4f0d-bcb7-4a58fa9643e3@intel.com>
Date: Thu, 3 Jul 2025 07:25:25 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Adrian Hunter <adrian.hunter@...el.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, pbonzini@...hat.com,
 seanjc@...gle.com, vannapurve@...gle.com
Cc: Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 x86@...nel.org, H Peter Anvin <hpa@...or.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, rick.p.edgecombe@...el.com,
 kirill.shutemov@...ux.intel.com, kai.huang@...el.com,
 reinette.chatre@...el.com, xiaoyao.li@...el.com,
 tony.lindgren@...ux.intel.com, binbin.wu@...ux.intel.com,
 isaku.yamahata@...el.com, yan.y.zhao@...el.com, chao.gao@...el.com
Subject: Re: [PATCH 2/2] x86/tdx: Skip clearing reclaimed pages unless
 X86_BUG_TDX_PW_MCE is present

On 7/3/25 04:40, Adrian Hunter wrote:
> @@ -642,6 +642,15 @@ static void reset_tdx_pages(unsigned long base, unsigned long size)
>  	const void *zero_page = (const void *)page_address(ZERO_PAGE(0));
>  	unsigned long phys, end;

If the only possible use for reset_tdx_pages() is for the erratum, then
it needs to be in the function name.

> +	/*
> +	 * Linux uses only KeyID 0 which can read or write pages
> +	 * that were formerly TDX private pages, without poisoning
> +	 * memory. However on platforms with the partial-write errata,
> +	 * poisoning still happens for partial writes.
> +	 */
> +	if (!boot_cpu_has_bug(X86_BUG_TDX_PW_MCE))
> +		return;

Would this be more clear?

	/*
	 * Typically, any write to the page will convert it from TDX
	 * private back to normal kernel memory. Systems with the
	 * erratum need to do the conversion explicitly.
	 */