linux-kernel - [RFC 1/1] x86/vmemmap: Add missing update of PML4 table / PML5 table entry

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Message-ID: <20250214195151.168306-2-gwan-gyeong.mun@intel.com>
Date: Fri, 14 Feb 2025 21:51:51 +0200
From: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
To: linux-kernel@...r.kernel.org
Cc: osalvador@...e.de,
	42.hyeyoo@...il.com,
	byungchul@...com,
	dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	akpm@...ux-foundation.org,
	max.byungchul.park@...com,
	max.byungchul.park@...il.com
Subject: [RFC 1/1] x86/vmemmap: Add missing update of PML4 table / PML5 table entry

when performing vmemmap populate, if the entry of the PML4 table/PML5 table
pointing to the target virtual address has never been updated, a page fault
occurs when the memset(start) called from the vmemmap_use_new_sub_pmd()
execution flow.

This fixes the problem of using the virtual address without updating the
entry in the PML4 table or PML5 table. But this is a temporary solution to
prevent page fault problems, and it requires improvement of the routine
that updates the missing entry in the PML4 table or PML5 table.

Fixes: faf1c0008a33 ("x86/vmemmap: optimize for consecutive sections in partial populated PMDs")
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: Byungchul Park <byungchul@...com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 arch/x86/mm/init_64.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 01ea7c6df303..7a4d8cea1a2e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -912,6 +912,7 @@ static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long
 {
 	const unsigned long page = ALIGN_DOWN(start, PMD_SIZE);
 
+	sync_global_pgds(start, end - 1);
 	vmemmap_flush_unused_pmd();
 
 	/*
-- 
2.48.1