From d56a8ea400a7de2a81d4fcfaa70c4b2f347c1ebf Mon Sep 17 00:00:00 2001 From: Jan Engelhardt 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 Signed-off-by: Jan Engelhardt Signed-off-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/acpi/boot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 3b20607d581b5..7303bb398862c 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -1752,7 +1752,7 @@ 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) -- 2.47.3