arm64: Add override for MPAM

JIRA: https://issues.redhat.com/browse/RHEL-92805

As the message of the commit 09e6b30 ("arm64: cpufeature: discover
CPU support for MPAM") already states, if a buggy firmware fails to
either enable MPAM or emulate the trap as if it were disabled, the
kernel will just fail to boot.  While upgrading the firmware should be
the best solution, we have some hardware of which the vendor have made
no response 2 months after we requested a firmware update.  Allow
overriding it so our devices don't become some e-waste.

Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Cc: Mingcong Bai <jeffbai@aosc.io>
Cc: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Cc: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250602043723.216338-1-xry111@xry111.site
Signed-off-by: Will Deacon <will@kernel.org>
(cherry picked from commit 10f885d)
Signed-off-by: Sebastian Ott <sebott@redhat.com>

Author: Sebastian Ott

Documentation/admin-guide/kernel-parameters.txt

@@ -452,6 +452,9 @@
 	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
 

arch/arm64/include/asm/el2_setup.h

@@ -294,19 +294,6 @@
 .Lskip_gcs_\@:
 .endm
 
-.macro __init_el2_mpam
-	/* Memory Partitioning And Monitoring: disable EL2 traps */
-	mrs	x1, id_aa64pfr0_el1
-	ubfx	x0, x1, #ID_AA64PFR0_EL1_MPAM_SHIFT, #4
-	cbz	x0, .Lskip_mpam_\@		// skip if no MPAM
-	msr_s	SYS_MPAM2_EL2, xzr		// use the default partition
-						// and disable lower traps
-	mrs_s	x0, SYS_MPAMIDR_EL1
-	tbz	x0, #MPAMIDR_EL1_HAS_HCR_SHIFT, .Lskip_mpam_\@	// skip if no MPAMHCR reg
-	msr_s	SYS_MPAMHCR_EL2, xzr		// clear TRAP_MPAMIDR_EL1 -> EL2
-.Lskip_mpam_\@:
-.endm
-
 /**
  * Initialize EL2 registers to sane values. This should be called early on all
  * cores that were booted in EL2. Note that everything gets initialised as
@@ -324,7 +311,6 @@
 	__init_el2_stage2
 	__init_el2_gicv3
 	__init_el2_hstr
-	__init_el2_mpam
 	__init_el2_nvhe_idregs
 	__init_el2_cptr
 	__init_el2_fgt
@@ -371,6 +357,16 @@
 #endif
 
 .macro finalise_el2_state
+	check_override id_aa64pfr0, ID_AA64PFR0_EL1_MPAM_SHIFT, .Linit_mpam_\@, .Lskip_mpam_\@, x1, x2
+
+.Linit_mpam_\@:
+	msr_s	SYS_MPAM2_EL2, xzr		// use the default partition
+						// and disable lower traps
+	mrs_s	x0, SYS_MPAMIDR_EL1
+	tbz	x0, #MPAMIDR_EL1_HAS_HCR_SHIFT, .Lskip_mpam_\@  // skip if no MPAMHCR reg
+	msr_s   SYS_MPAMHCR_EL2, xzr		// clear TRAP_MPAMIDR_EL1 -> EL2
+
+.Lskip_mpam_\@:
 	check_override id_aa64pfr0, ID_AA64PFR0_EL1_SVE_SHIFT, .Linit_sve_\@, .Lskip_sve_\@, x1, x2
 
 .Linit_sve_\@:	/* SVE register access */

arch/arm64/kernel/cpufeature.c

@@ -1192,8 +1192,10 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
 		cpacr_restore(cpacr);
 	}
 
-	if (id_aa64pfr0_mpam(info->reg_id_aa64pfr0))
+	if (id_aa64pfr0_mpam(read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1))) {
+		info->reg_mpamidr = read_cpuid(MPAMIDR_EL1);
 		init_cpu_ftr_reg(SYS_MPAMIDR_EL1, info->reg_mpamidr);
+	}
 
 	if (id_aa64pfr1_mte(info->reg_id_aa64pfr1))
 		init_cpu_ftr_reg(SYS_GMID_EL1, info->reg_gmid);
@@ -1444,7 +1446,8 @@ void update_cpu_features(int cpu,
 		cpacr_restore(cpacr);
 	}
 
-	if (id_aa64pfr0_mpam(info->reg_id_aa64pfr0)) {
+	if (id_aa64pfr0_mpam(read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1))) {
+		info->reg_mpamidr = read_cpuid(MPAMIDR_EL1);
 		taint |= check_update_ftr_reg(SYS_MPAMIDR_EL1, cpu,
 					info->reg_mpamidr, boot->reg_mpamidr);
 	}

arch/arm64/kernel/cpuinfo.c

@@ -494,8 +494,11 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
 	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0))
 		__cpuinfo_store_cpu_32bit(&info->aarch32);
 
-	if (id_aa64pfr0_mpam(info->reg_id_aa64pfr0))
-		info->reg_mpamidr = read_cpuid(MPAMIDR_EL1);
+	/*
+	 * info->reg_mpamidr deferred to {init,update}_cpu_features because we
+	 * don't want to read it (and trigger a trap on buggy firmware) if
+	 * using an aa64pfr0_el1 override to unconditionally disable MPAM.
+	 */
 
 	if (IS_ENABLED(CONFIG_ARM64_SME) &&
 	    id_aa64pfr1_sme(info->reg_id_aa64pfr1)) {

arch/arm64/kernel/pi/idreg-override.c

@@ -127,6 +127,7 @@ static const struct ftr_set_desc pfr0 __prel64_initconst = {
 	.fields		= {
 	        FIELD("sve", ID_AA64PFR0_EL1_SVE_SHIFT, pfr0_sve_filter),
 		FIELD("el0", ID_AA64PFR0_EL1_EL0_SHIFT, NULL),
+		FIELD("mpam", ID_AA64PFR0_EL1_MPAM_SHIFT, NULL),
 		{}
 	},
 };
@@ -154,6 +155,7 @@ static const struct ftr_set_desc pfr1 __prel64_initconst = {
 		FIELD("gcs", ID_AA64PFR1_EL1_GCS_SHIFT, NULL),
 		FIELD("mte", ID_AA64PFR1_EL1_MTE_SHIFT, NULL),
 		FIELD("sme", ID_AA64PFR1_EL1_SME_SHIFT, pfr1_sme_filter),
+		FIELD("mpam_frac", ID_AA64PFR1_EL1_MPAM_frac_SHIFT, NULL),
 		{}
 	},
 };
@@ -246,6 +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" },
 };
 
 static int __init parse_hexdigit(const char *p, u64 *v)