From: tanze <tanze@kylinos.cn>

In practical application scenarios, some manufacturers use outdated
firmware and do not add relevant configurations to the kernel command
line during deployment, which will result in system boot failure.
For manufacturers, disabling the MPAM feature by default and
enabling it via additional boot parameters only when required
is a more effective way to ensure compatibility.

Fixes: 10f885d63a0e ("arm64: Add override for MPAM")
Signed-off-by: tanze <tanze@kylinos.cn>
---
 Documentation/admin-guide/kernel-parameters.txt | 6 +++---
 arch/arm64/kernel/pi/idreg-override.c           | 8 +++++++-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a8d0afde7f85..c10d9529147c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -556,9 +556,6 @@ Kernel parameters
 	arm64.nomops	[ARM64] Unconditionally disable Memory Copy and Memory
 			Set instructions support
 
-	arm64.nompam	[ARM64] Unconditionally disable Memory Partitioning And
-			Monitoring support
-
 	arm64.nomte	[ARM64] Unconditionally disable Memory Tagging Extension
 			support
 
@@ -571,6 +568,9 @@ Kernel parameters
 	arm64.nosve	[ARM64] Unconditionally disable Scalable Vector
 			Extension support
 
+	arm64.mpam	[ARM64] Unconditionally enable Memory Partitioning And
+			Monitoring 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 bc57b290e5e7..f4e3972155c4 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -248,7 +248,7 @@ static const struct {
 	{ "rodata=off",			"arm64_sw.rodataoff=1" },
 	{ "arm64.nolva",		"id_aa64mmfr2.varange=0" },
 	{ "arm64.no32bit_el0",		"id_aa64pfr0.el0=1" },
-	{ "arm64.nompam",		"id_aa64pfr0.mpam=0 id_aa64pfr1.mpam_frac=0" },
+	{ "arm64.mpam",			"id_aa64pfr0.mpam=1 id_aa64pfr1.mpam_frac=1" },
 };
 
 static int __init parse_hexdigit(const char *p, u64 *v)
@@ -409,6 +409,12 @@ void __init init_feature_override(u64 boot_status, const void *fdt,
 
 	__boot_status = boot_status;
 
+	/*
+	 * Set the boot parameter to disable the MPAM feature,
+	 * thus avoiding system boot failure.
+	 */
+	match_options("id_aa64pfr0.mpam=0 id_aa64pfr1.mpam_frac=0");
+
 	parse_cmdline(fdt, chosen);
 
 	for (i = 0; i < ARRAY_SIZE(regs); i++) {
-- 
2.25.1

On Wed, 17 Dec 2025 15:11:59 +0000,
tanze@kylinos.cn wrote:
> 
> From: tanze <tanze@kylinos.cn>
> 
> In practical application scenarios, some manufacturers use outdated
> firmware and do not add relevant configurations to the kernel command
> line during deployment, which will result in system boot failure.
> For manufacturers, disabling the MPAM feature by default and
> enabling it via additional boot parameters only when required
> is a more effective way to ensure compatibility.

No. I don't see the need to be overly cooperative with people who do
not care about what they ship.

If you want to run on broken systems, pass the option that allow you
to do so. But don't make it more complicated for people who have HW
that actually works.

I would rather remove the option to disable MPAM altogether and leave
these broken systems completely unsupported.

	M.

-- 
Without deviation from the norm, progress is not possible.