linux-kernel - [tip: x86/mm] x86/mm: Always "broadcast" PMD setting operations

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Message-ID: <174491300802.31282.1389796894467957175.tip-bot2@tip-bot2>
Date: Thu, 17 Apr 2025 18:03:28 -0000
From: "tip-bot2 for Dave Hansen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/mm] x86/mm: Always "broadcast" PMD setting operations

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     b0cc4d19f198cdfd1b58c8f5536670d1dc68cbbd
Gitweb:        https://git.kernel.org/tip/b0cc4d19f198cdfd1b58c8f5536670d1dc68cbbd
Author:        Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate:    Mon, 14 Apr 2025 10:32:35 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Thu, 17 Apr 2025 10:39:25 -07:00

x86/mm: Always "broadcast" PMD setting operations

Kernel PMDs can either be shared across processes or private to a
process.  On 64-bit, they are always shared.  32-bit non-PAE hardware
does not have PMDs, but the kernel logically squishes them into the
PGD and treats them as private. Here are the four cases:

	64-bit:                Shared
	32-bit: non-PAE:       Private
	32-bit:     PAE+  PTI: Private
	32-bit:     PAE+noPTI: Shared

Note that 32-bit is all "Private" except for PAE+noPTI being an
oddball.  The 32-bit+PAE+noPTI case will be made like the rest of
32-bit shortly.

But until that can be done, temporarily treat the 32-bit+PAE+noPTI
case as Private. This will do unnecessary walks across pgd_list and
unnecessary PTE setting but should be otherwise harmless.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lore.kernel.org/all/20250414173235.F63F50D1%40davehans-spike.ostc.intel.com
---
 arch/x86/mm/pat/set_memory.c |  4 ++--
 arch/x86/mm/pgtable.c        | 11 +++--------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index def3d92..30ab4ac 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -889,7 +889,7 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
 	/* change init_mm */
 	set_pte_atomic(kpte, pte);
 #ifdef CONFIG_X86_32
-	if (!SHARED_KERNEL_PMD) {
+	{
 		struct page *page;
 
 		list_for_each_entry(page, &pgd_list, lru) {
@@ -1293,7 +1293,7 @@ static int collapse_pmd_page(pmd_t *pmd, unsigned long addr,
 	/* Queue the page table to be freed after TLB flush */
 	list_add(&page_ptdesc(pmd_page(old_pmd))->pt_list, pgtables);
 
-	if (IS_ENABLED(CONFIG_X86_32) && !SHARED_KERNEL_PMD) {
+	if (IS_ENABLED(CONFIG_X86_32)) {
 		struct page *page;
 
 		/* Update all PGD tables to use the same large page */
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index ea01b55..f1c5886 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -97,18 +97,13 @@ static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
 				KERNEL_PGD_PTRS);
 	}
 
-	/* list required to sync kernel mapping updates */
-	if (!SHARED_KERNEL_PMD) {
-		pgd_set_mm(pgd, mm);
-		pgd_list_add(pgd);
-	}
+	/* List used to sync kernel mapping updates */
+	pgd_set_mm(pgd, mm);
+	pgd_list_add(pgd);
 }
 
 static void pgd_dtor(pgd_t *pgd)
 {
-	if (SHARED_KERNEL_PMD)
-		return;
-
 	spin_lock(&pgd_lock);
 	pgd_list_del(pgd);
 	spin_unlock(&pgd_lock);