linux-kernel - [tip: x86/mm] x86/mm: Fix up comments around PMD preallocation

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Message-ID: <174491300601.31282.7910421211046512242.tip-bot2@tip-bot2>
Date: Thu, 17 Apr 2025 18:03:26 -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: Fix up comments around PMD preallocation

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

Commit-ID:     82f120010f3b86c2f9c1279452c1ecab7bc117d2
Gitweb:        https://git.kernel.org/tip/82f120010f3b86c2f9c1279452c1ecab7bc117d2
Author:        Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate:    Mon, 14 Apr 2025 10:32:40 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Thu, 17 Apr 2025 10:39:25 -07:00

x86/mm: Fix up comments around PMD preallocation

The "paravirt environment" is no longer in the tree. Axe that part of the
comment. Also add a blurb to remind readers that "USER_PMDS" refer to
the PTI user *copy* of the page tables, not the user *portion*.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lore.kernel.org/all/20250414173240.5B1AB322%40davehans-spike.ostc.intel.com
---
 arch/x86/mm/pgtable.c |  9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 027e1d3..ca07db5 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -121,16 +121,17 @@ static void pgd_dtor(pgd_t *pgd)
  * processor notices the update.  Since this is expensive, and
  * all 4 top-level entries are used almost immediately in a
  * new process's life, we just pre-populate them here.
- *
- * Also, if we're in a paravirt environment where the kernel pmd is
- * not shared between pagetables (!SHARED_KERNEL_PMDS), we allocate
- * and initialize the kernel pmds here.
  */
 #define PREALLOCATED_PMDS	(static_cpu_has(X86_FEATURE_PTI) ? \
 					PTRS_PER_PGD : KERNEL_PGD_BOUNDARY)
 #define MAX_PREALLOCATED_PMDS	PTRS_PER_PGD
 
 /*
+ * "USER_PMDS" are the PMDs for the user copy of the page tables when
+ * PTI is enabled. They do not exist when PTI is disabled.  Note that
+ * this is distinct from the user _portion_ of the kernel page tables
+ * which always exists.
+ *
  * We allocate separate PMDs for the kernel part of the user page-table
  * when PTI is enabled. We need them to map the per-process LDT into the
  * user-space page-table.