linux-kernel - Re: [PATCH V4 1/2] x86/tdx: Eliminate duplicate code in tdx_clear

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Message-ID: <f7f99ab69867a547e3d7ef4f73a9307c3874ad6f.camel@intel.com>
Date: Wed, 23 Jul 2025 14:06:00 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Annapurve, Vishal" <vannapurve@...gle.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "Hunter, Adrian" <adrian.hunter@...el.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "Huang, Kai" <kai.huang@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "Luck, Tony" <tony.luck@...el.com>, "kas@...nel.org"
	<kas@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "tony.lindgren@...ux.intel.com"
	<tony.lindgren@...ux.intel.com>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "binbin.wu@...ux.intel.com"
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	<bp@...en8.de>, "Gao, Chao" <chao.gao@...el.com>, "x86@...nel.org"
	<x86@...nel.org>
Subject: Re: [PATCH V4 1/2] x86/tdx: Eliminate duplicate code in
 tdx_clear_page()

On Wed, 2025-07-23 at 15:05 +0300, Adrian Hunter wrote:
>  
> +void tdx_quirk_reset_page(struct page *page)
> +{
> +	tdx_quirk_reset_paddr(page_to_phys(page), PAGE_SIZE);
> +}
> +EXPORT_SYMBOL_GPL(tdx_quirk_reset_page);
> +
>  static void tdmr_reset_pamt(struct tdmr_info *tdmr)
>  {
> -	tdmr_do_pamt_func(tdmr, reset_tdx_pages);
> +	tdmr_do_pamt_func(tdmr, tdx_quirk_reset_paddr);
>  }
>  

Up the call chain there is:
	/*
	 * According to the TDX hardware spec, if the platform
	 * doesn't have the "partial write machine check"
	 * erratum, any kernel read/write will never cause #MC
	 * in kernel space, thus it's OK to not convert PAMTs
	 * back to normal.  But do the conversion anyway here
	 * as suggested by the TDX spec.
	 */
	tdmrs_reset_pamt_all(&tdx_tdmr_list);


So the comment says it's going to clear it even if partial write machine check
is not present. Then the call chain goes through a bunch of functions not named
"quirk", then finally calls "tdx_quirk_reset_paddr" which actually skips the
page clearing.

I think you need to either fix the comment and rename the whole stack to
"tdx_quirk_...", or make tdx_quirk_reset_page() be the one that has the errata
check, and the error path above call the PA version reset_tdx_pages() without
the errata check.

The latter seems better to me for the sake of less churn.