From bb3b2cfeb206f5b10b859e134651b54120e3f530 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Tue, 30 Jun 2026 18:05:56 +0100 Subject: [PATCH] ARM: 9480/1: entry: expand comment in __switch_to As per discussion between the developers in the mail thread linked, expand the comment in __switch_to so that readers of the code understand what is going on. Suggested-by: Mark Rutland Acked-by: Mark Rutland Signed-off-by: Linus Walleij > Signed-off-by: Russell King --- arch/arm/kernel/entry-armv.S | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index ef6a657c8d13..b7faefe5bce7 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -557,9 +557,16 @@ ENTRY(__switch_to) ldmia r4, {r4 - sl, fp, ip, lr} @ Load all regs saved previously #ifdef CONFIG_VMAP_STACK @ - @ Do a dummy read from the new stack while running from the old one so - @ that we can rely on do_translation_fault() to fix up any stale PMD - @ entries covering the vmalloc region. + @ For a non-lazy mm switch, check_vmalloc_seq() has ensured that + @ that the active mm's page tables have mappings for the prev + @ task's stack and the next task's stack. + @ + @ For a lazy mm switch the active mm's page tables have mappings + @ for the prev task's stack but might not have mappings for the + @ new task's stack. Do a dummy read from the new stack while + @ running from the old stack so that we can rely on + @ do_translation_fault() to populate missing PMD entries covering the + @ new task's stack in the old task's page tables. @ ldr r2, [ip] #ifdef CONFIG_KASAN_VMALLOC