linux-kernel - [RFC][PATCH 4/8] x86/mm: Simplify PAE PGD sharing macros

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Message-Id: <20250123172435.270F7BAC@davehans-spike.ostc.intel.com>
Date: Thu, 23 Jan 2025 09:24:35 -0800
From: Dave Hansen <dave.hansen@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,tglx@...utronix.de,bp@...en8.de,joro@...tes.org,luto@...nel.org,peterz@...radead.org,kirill.shutemov@...ux.intel.com,rick.p.edgecombe@...el.com,jgross@...e.com,Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [RFC][PATCH 4/8] x86/mm: Simplify PAE PGD sharing macros


From: Dave Hansen <dave.hansen@...ux.intel.com>

There are a few too many levels of abstraction here.

First, just expand the PREALLOCATED_PMDS macro in place to make it
clear that it is only conditional on PTI.

Second, MAX_PREALLOCATED_PMDS is only used in one spot for an
on-stack allocation. It has a *maximum* value of 4. Do not bother
with the macro MAX() magic.  Just set it to 4.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
---

 b/arch/x86/mm/pgtable.c |   11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff -puN arch/x86/mm/pgtable.c~simplify-PREALLOCATED_PMDS arch/x86/mm/pgtable.c
--- a/arch/x86/mm/pgtable.c~simplify-PREALLOCATED_PMDS	2025-01-23 09:20:51.626382013 -0800
+++ b/arch/x86/mm/pgtable.c	2025-01-23 09:20:51.630382157 -0800
@@ -107,12 +107,6 @@ static inline void pgd_list_del(pgd_t *p
 	list_del(&ptdesc->pt_list);
 }
 
-#define UNSHARED_PTRS_PER_PGD				\
-	(SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)
-#define MAX_UNSHARED_PTRS_PER_PGD			\
-	MAX_T(size_t, KERNEL_PGD_BOUNDARY, PTRS_PER_PGD)
-
-
 static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm)
 {
 	virt_to_ptdesc(pgd)->pt_mm = mm;
@@ -171,8 +165,9 @@ static void pgd_dtor(pgd_t *pgd)
  * not shared between pagetables (!SHARED_KERNEL_PMDS), we allocate
  * and initialize the kernel pmds here.
  */
-#define PREALLOCATED_PMDS	UNSHARED_PTRS_PER_PGD
-#define MAX_PREALLOCATED_PMDS	MAX_UNSHARED_PTRS_PER_PGD
+#define PREALLOCATED_PMDS	(static_cpu_has(X86_FEATURE_PTI) ? \
+					PTRS_PER_PGD : KERNEL_PGD_BOUNDARY)
+#define MAX_PREALLOCATED_PMDS	PTRS_PER_PGD
 
 /*
  * We allocate separate PMDs for the kernel part of the user page-table
_