Add an override for WFxT support within ID_AA64ISAR2_EL1 to allow
it to be disabled using the new arm64.nowfxt command line parameter.

This accompanies the idle=nop param introduced in a previous patch
series [1] in dealing with misbehaving WFI and WFIT instructions on
Apple Silicon SoCs, and eases debugging of other quirky WFxT
implementations.

Link[1]: https://lore.kernel.org/all/20260804-arm64-idle-param-v3-1-d10f8159062b@cyberchaos.dev/
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Yureka Lilian <yureka@cyberchaos.dev>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 arch/arm64/kernel/pi/idreg-override.c           | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb5251242311..6a35623e4a17 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -587,6 +587,9 @@ Kernel parameters
 	arm64.nosve	[ARM64] Unconditionally disable Scalable Vector
 			Extension support
 
+	arm64.nowfxt    [ARM64] Unconditionally disable Wait For Event with
+			Timeout and Wait For Interrupt with Timeout support
+
 	ataflop=	[HW,M68k]
 
 	atarimouse=	[HW,MOUSE] Atari Mouse
diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
index 274bc72ba98d..acaf56234973 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -186,6 +186,7 @@ static const struct ftr_set_desc isar2 __prel64_initconst = {
 	.name		= "id_aa64isar2",
 	.override	= &id_aa64isar2_override,
 	.fields		= {
+		FIELD("wfxt", ID_AA64ISAR2_EL1_WFxT_SHIFT, NULL),
 		FIELD("gpa3", ID_AA64ISAR2_EL1_GPA3_SHIFT, NULL),
 		FIELD("apa3", ID_AA64ISAR2_EL1_APA3_SHIFT, NULL),
 		FIELD("mops", ID_AA64ISAR2_EL1_MOPS_SHIFT, NULL),
@@ -254,6 +255,7 @@ static const struct {
 	  "id_aa64isar1.api=0 id_aa64isar1.apa=0 "
 	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
 	{ "arm64.nomops",		"id_aa64isar2.mops=0" },
+	{ "arm64.nowfxt",		"id_aa64isar2.wfxt=0" },
 	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
 	{ "nokaslr",			"arm64_sw.nokaslr=1" },
 	{ "rodata=off",			"arm64_sw.rodataoff=1" },

---
base-commit: 5e6de6a2b522f659defacb1551d0465ba6ce13cf
change-id: 20260811-idreg-override-wfxt-b2633fd4d04f

Best regards,
--  
Yureka Lilian <yureka@cyberchaos.dev>

On Fri, 11 Sep 2026 19:02:10 +0200, Yureka Lilian wrote:
> Add an override for WFxT support within ID_AA64ISAR2_EL1 to allow
> it to be disabled using the new arm64.nowfxt command line parameter.
> 
> This accompanies the idle=nop param introduced in a previous patch
> series [1] in dealing with misbehaving WFI and WFIT instructions on
> Apple Silicon SoCs, and eases debugging of other quirky WFxT
> implementations.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: Add override for WFxT
      https://git.kernel.org/arm64/c/baaa9b126b87

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev