arm64: Add the arm64.nosve command line option

In order to be able to completely disable SVE even if the HW
seems to support it (most likely because the FW is broken),
move the SVE setup into the EL2 finalisation block, and
use a new idreg override to deal with it.

Note that we also nuke id_aa64zfr0_el1 as a byproduct, and
that SME also gets disabled, due to the dependency between the
two features.

Signed-off-by: Marc Zyngier <[email protected]>
Reviewed-by: Mark Brown <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Marc Zyngier

Documentation/admin-guide/kernel-parameters.txt

@@ -400,6 +400,9 @@
 	arm64.nomte	[ARM64] Unconditionally disable Memory Tagging Extension
 			support
 
+	arm64.nosve	[ARM64] Unconditionally disable Scalable Vector
+			Extension support
+
 	arm64.nosme	[ARM64] Unconditionally disable Scalable Matrix
 			Extension support
 

arch/arm64/include/asm/cpufeature.h

@@ -908,7 +908,9 @@ static inline unsigned int get_vmid_bits(u64 mmfr1)
 }
 
 extern struct arm64_ftr_override id_aa64mmfr1_override;
+extern struct arm64_ftr_override id_aa64pfr0_override;
 extern struct arm64_ftr_override id_aa64pfr1_override;
+extern struct arm64_ftr_override id_aa64zfr0_override;
 extern struct arm64_ftr_override id_aa64smfr0_override;
 extern struct arm64_ftr_override id_aa64isar1_override;
 extern struct arm64_ftr_override id_aa64isar2_override;

arch/arm64/include/asm/el2_setup.h

@@ -129,20 +129,6 @@
 	msr	cptr_el2, x0			// Disable copro. traps to EL2
 .endm
 
-/* SVE register access */
-.macro __init_el2_nvhe_sve
-	mrs	x1, id_aa64pfr0_el1
-	ubfx	x1, x1, #ID_AA64PFR0_SVE_SHIFT, #4
-	cbz	x1, .Lskip_sve_\@
-
-	bic	x0, x0, #CPTR_EL2_TZ		// Also disable SVE traps
-	msr	cptr_el2, x0			// Disable copro. traps to EL2
-	isb
-	mov	x1, #ZCR_ELx_LEN_MASK		// SVE: Enable full vector
-	msr_s	SYS_ZCR_EL2, x1			// length for EL1.
-.Lskip_sve_\@:
-.endm
-
 /* Disable any fine grained traps */
 .macro __init_el2_fgt
 	mrs	x1, id_aa64mmfr0_el1
@@ -206,7 +192,6 @@
 	__init_el2_hstr
 	__init_el2_nvhe_idregs
 	__init_el2_nvhe_cptr
-	__init_el2_nvhe_sve
 	__init_el2_fgt
 	__init_el2_nvhe_prepare_eret
 .endm

arch/arm64/kernel/cpufeature.c

@@ -631,7 +631,9 @@ static const struct arm64_ftr_bits ftr_raz[] = {
 	__ARM64_FTR_REG_OVERRIDE(#id, id, table, &no_override)
 
 struct arm64_ftr_override __ro_after_init id_aa64mmfr1_override;
+struct arm64_ftr_override __ro_after_init id_aa64pfr0_override;
 struct arm64_ftr_override __ro_after_init id_aa64pfr1_override;
+struct arm64_ftr_override __ro_after_init id_aa64zfr0_override;
 struct arm64_ftr_override __ro_after_init id_aa64smfr0_override;
 struct arm64_ftr_override __ro_after_init id_aa64isar1_override;
 struct arm64_ftr_override __ro_after_init id_aa64isar2_override;
@@ -669,10 +671,12 @@ static const struct __ftr_reg_entry {
 	ARM64_FTR_REG(SYS_ID_MMFR5_EL1, ftr_id_mmfr5),
 
 	/* Op1 = 0, CRn = 0, CRm = 4 */
-	ARM64_FTR_REG(SYS_ID_AA64PFR0_EL1, ftr_id_aa64pfr0),
+	ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64PFR0_EL1, ftr_id_aa64pfr0,
+			       &id_aa64pfr0_override),
 	ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64PFR1_EL1, ftr_id_aa64pfr1,
 			       &id_aa64pfr1_override),
-	ARM64_FTR_REG(SYS_ID_AA64ZFR0_EL1, ftr_id_aa64zfr0),
+	ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64ZFR0_EL1, ftr_id_aa64zfr0,
+			       &id_aa64zfr0_override),
 	ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64SMFR0_EL1, ftr_id_aa64smfr0,
 			       &id_aa64smfr0_override),
 

arch/arm64/kernel/hyp-stub.S

@@ -98,6 +98,17 @@ SYM_CODE_START_LOCAL(elx_sync)
 SYM_CODE_END(elx_sync)
 
 SYM_CODE_START_LOCAL(__finalise_el2)
+	check_override id_aa64pfr0 ID_AA64PFR0_SVE_SHIFT .Linit_sve .Lskip_sve
+
+.Linit_sve:	/* SVE register access */
+	mrs	x0, cptr_el2			// Disable SVE traps
+	bic	x0, x0, #CPTR_EL2_TZ
+	msr	cptr_el2, x0
+	isb
+	mov	x1, #ZCR_ELx_LEN_MASK		// SVE: Enable full vector
+	msr_s	SYS_ZCR_EL2, x1			// length for EL1.
+
+.Lskip_sve:
 	check_override id_aa64pfr1 ID_AA64PFR1_SME_SHIFT .Linit_sme .Lskip_sme
 
 .Linit_sme:	/* SME register access and priority mapping */

arch/arm64/kernel/idreg-override.c

@@ -55,6 +55,30 @@ static const struct ftr_set_desc mmfr1 __initconst = {
 	},
 };
 
+static bool __init pfr0_sve_filter(u64 val)
+{
+	/*
+	 * Disabling SVE also means disabling all the features that
+	 * are associated with it. The easiest way to do it is just to
+	 * override id_aa64zfr0_el1 to be 0.
+	 */
+	if (!val) {
+		id_aa64zfr0_override.val = 0;
+		id_aa64zfr0_override.mask = GENMASK(63, 0);
+	}
+
+	return true;
+}
+
+static const struct ftr_set_desc pfr0 __initconst = {
+	.name		= "id_aa64pfr0",
+	.override	= &id_aa64pfr0_override,
+	.fields		= {
+	        FIELD("sve", ID_AA64PFR0_SVE_SHIFT, pfr0_sve_filter),
+		{}
+	},
+};
+
 static bool __init pfr1_sme_filter(u64 val)
 {
 	/*
@@ -118,6 +142,7 @@ static const struct ftr_set_desc kaslr __initconst = {
 
 static const struct ftr_set_desc * const regs[] __initconst = {
 	&mmfr1,
+	&pfr0,
 	&pfr1,
 	&isar1,
 	&isar2,
@@ -130,6 +155,7 @@ static const struct {
 } aliases[] __initconst = {
 	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
+	{ "arm64.nosve",		"id_aa64pfr0.sve=0 id_aa64pfr1.sme=0" },
 	{ "arm64.nosme",		"id_aa64pfr1.sme=0" },
 	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
 	{ "arm64.nopauth",