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

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Message-ID: <ee2f8d16-be3c-403e-8b9c-e5bec6d010ce@intel.com>
Date: Wed, 23 Jul 2025 17:37:33 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "pbonzini@...hat.com" <pbonzini@...hat.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"
	<binbin.wu@...ux.intel.com>, "hpa@...or.com" <hpa@...or.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 17:06, Edgecombe, Rick P wrote:
> 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.

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.

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