blob: 6b4e0ebe6d4e136d0fa6b2b1b330111821ad307c [file] [log] [blame]
From 4a1ca60cbf1579e820197d2248f46b75a87d4cb7 Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <jengelh@inai.de>
Date: Thu, 5 Mar 2020 13:24:25 +0100
Subject: [PATCH] acpi/x86: ignore unspecified bit positions in the ACPI global
lock field
commit ecb9c790999fd6c5af0f44783bd0217f0b89ec2b upstream.
The value in "new" is constructed from "old" such that all bits defined
as reserved by the ACPI spec[1] are left untouched. But if those bits
do not happen to be all zero, "new < 3" will not evaluate to true.
The firmware of the laptop(s) Medion MD63490 / Akoya P15648 comes with
garbage inside the "FACS" ACPI table. The starting value is
old=0x4944454d, therefore new=0x4944454e, which is >= 3. Mask off
the reserved bits.
[1] https://uefi.org/sites/default/files/resources/ACPI_6_2.pdf
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206553
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 17b33ef604f3..ea019ba02942 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -1740,7 +1740,7 @@ int __acpi_acquire_global_lock(unsigned int *lock)
new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1));
val = cmpxchg(lock, old, new);
} while (unlikely (val != old));
- return (new < 3) ? -1 : 0;
+ return ((new & 0x3) < 3) ? -1 : 0;
}
int __acpi_release_global_lock(unsigned int *lock)
--
2.7.4