From bb3b2cfeb206f5b10b859e134651b54120e3f530 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Tue, 30 Jun 2026 18:05:56 +0100 Subject: 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 --- lib/devmem_is_allowed.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) create mode 100644 lib/devmem_is_allowed.c (limited to 'lib/devmem_is_allowed.c') diff --git a/lib/devmem_is_allowed.c b/lib/devmem_is_allowed.c new file mode 100644 index 000000000..9c060c69f --- /dev/null +++ b/lib/devmem_is_allowed.c @@ -0,0 +1,28 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * A generic version of devmem_is_allowed. + * + * Based on arch/arm64/mm/mmap.c + * + * Copyright (C) 2020 Google, Inc. + * Copyright (C) 2012 ARM Ltd. + */ + +#include +#include +#include + +/* + * devmem_is_allowed() checks to see if /dev/mem access to a certain address + * is valid. The argument is a physical page number. We mimic x86 here by + * disallowing access to system RAM as well as device-exclusive MMIO regions. + * This effectively disable read()/write() on /dev/mem. + */ +int devmem_is_allowed(unsigned long pfn) +{ + if (iomem_is_exclusive(PFN_PHYS(pfn))) + return 0; + if (!page_is_ram(pfn)) + return 1; + return 0; +} -- cgit v1.3.1