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

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Message-ID: <7e54649c-7eb2-444f-849b-7ced20a5bb05@intel.com>
Date: Wed, 23 Jul 2025 18:30:43 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "Annapurve, Vishal" <vannapurve@...gle.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>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tony.lindgren@...ux.intel.com" <tony.lindgren@...ux.intel.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "kas@...nel.org" <kas@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de" <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 23/07/2025 17:44, Edgecombe, Rick P wrote:
> On Wed, 2025-07-23 at 17:37 +0300, Adrian Hunter wrote:
>>> The latter seems better to me for the sake of less churn.
>>
>> Why make tdx_quirk_reset_page() and tdx_quirk_reset_paddr() follow
>> different rules.
>>
>> How about this:
>>
>> From: Adrian Hunter <adrian.hunter@...el.com>
>> Subject: [PATCH] x86/tdx: Tidy reset_pamt functions
>>
>> Rename reset_pamt functions to contain "quirk" to reflect the new
>> functionality, and remove the now misleading comment.
> 
> This looks like the "former" option. Churn is not too bad, and it has the
> benefit of clear code vs long comment. I'm ok either way. But it needs to go
> cleanup first in the patch order.
> 
> The log should explain why it's ok to change now, with respect to the reasoning
> in the comment that is being removed.

It makes more sense afterwards because then it can refer to the
functional change:

From: Adrian Hunter <adrian.hunter@...el.com>
Subject: [PATCH] x86/tdx: Tidy reset_pamt functions

tdx_quirk_reset_paddr() has been made to reflect that, in fact, the
clearing is necessary only for hardware with a certain quirk.  Refer
patch "x86/tdx: Skip clearing reclaimed pages unless X86_BUG_TDX_PW_MCE
is present" for details.

Rename reset_pamt functions to contain "quirk" to reflect the new
functionality, and remove the now misleading comment.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 arch/x86/virt/vmx/tdx/tdx.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index ef22fc2b9af0..823850399bb7 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -664,17 +664,17 @@ void tdx_quirk_reset_page(struct page *page)
 }
 EXPORT_SYMBOL_GPL(tdx_quirk_reset_page);
 
-static void tdmr_reset_pamt(struct tdmr_info *tdmr)
+static void tdmr_quirk_reset_pamt(struct tdmr_info *tdmr)
 {
 	tdmr_do_pamt_func(tdmr, tdx_quirk_reset_paddr);
 }
 
-static void tdmrs_reset_pamt_all(struct tdmr_info_list *tdmr_list)
+static void tdmrs_quirk_reset_pamt_all(struct tdmr_info_list *tdmr_list)
 {
 	int i;
 
 	for (i = 0; i < tdmr_list->nr_consumed_tdmrs; i++)
-		tdmr_reset_pamt(tdmr_entry(tdmr_list, i));
+		tdmr_quirk_reset_pamt(tdmr_entry(tdmr_list, i));
 }
 
 static unsigned long tdmrs_count_pamt_kb(struct tdmr_info_list *tdmr_list)
@@ -1146,15 +1146,7 @@ static int init_tdx_module(void)
 	 * to the kernel.
 	 */
 	wbinvd_on_all_cpus();
-	/*
-	 * 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);
+	tdmrs_quirk_reset_pamt_all(&tdx_tdmr_list);
 err_free_pamts:
 	tdmrs_free_pamt_all(&tdx_tdmr_list);
 err_free_tdmrs:
-- 
2.48.1