arm64/sve: Detect SVE and activate runtime support

This patch enables detection of hardware SVE support via the
cpufeatures framework, and reports its presence to the kernel and
userspace via the new ARM64_SVE cpucap and HWCAP_SVE hwcap
respectively.

Userspace can also detect SVE using ID_AA64PFR0_EL1, using the
cpufeatures MRS emulation.

When running on hardware that supports SVE, this enables runtime
kernel support for SVE, and allows user tasks to execute SVE
instructions and make of the of the SVE-specific user/kernel
interface extensions implemented by this series.

Signed-off-by: Dave Martin <[e-mail]>
Reviewed-by: Suzuki K Poulose <[e-mail]>
Reviewed-by: Catalin Marinas <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>

Documentation/arm64/cpu-feature-registers.txt

···
      x--------------------------------------------------x
      | Name                         |  bits   | visible |
      |--------------------------------------------------|
-     | RES0                         | [63-28] |    n    |
+     | RES0                         | [63-36] |    n    |
+     |--------------------------------------------------|
+     | SVE                          | [35-32] |    y    |
+     |--------------------------------------------------|
+     | RES0                         | [31-28] |    n    |
      |--------------------------------------------------|
      | GIC                          | [27-24] |    n    |
      |--------------------------------------------------|

Documentation/arm64/elf_hwcaps.txt

···
 HWCAP_SHA512
 
     Functionality implied by ID_AA64ISAR0_EL1.SHA2 == 0b0002.
+
+HWCAP_SVE
+
+    Functionality implied by ID_AA64PFR0_EL1.SVE == 0b0001.

arch/arm64/include/asm/cpucaps.h

···
 #define ARM64_WORKAROUND_858921			19
 #define ARM64_WORKAROUND_CAVIUM_30115		20
 #define ARM64_HAS_DCPOP				21
+#define ARM64_SVE				22
 
-#define ARM64_NCAPS				22
+#define ARM64_NCAPS				23
 
 #endif /* __ASM_CPUCAPS_H */

arch/arm64/include/asm/cpufeature.h

···
 
 static inline bool system_supports_sve(void)
 {
-	return false;
+	return IS_ENABLED(CONFIG_ARM64_SVE) &&
+		cpus_have_const_cap(ARM64_SVE);
 }
 
 /*

arch/arm64/include/uapi/asm/hwcap.h

···
 #define HWCAP_SM4		(1 << 19)
 #define HWCAP_ASIMDDP		(1 << 20)
 #define HWCAP_SHA512		(1 << 21)
+#define HWCAP_SVE		(1 << 22)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

···
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_SVE_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_GIC_SHIFT, 4, 0),
 	S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
 	S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_FP_SHIFT, 4, ID_AA64PFR0_FP_NI),
···
 		.min_field_value = 1,
 	},
 #endif
+#ifdef CONFIG_ARM64_SVE
+	{
+		.desc = "Scalable Vector Extension",
+		.capability = ARM64_SVE,
+		.def_scope = SCOPE_SYSTEM,
+		.sys_reg = SYS_ID_AA64PFR0_EL1,
+		.sign = FTR_UNSIGNED,
+		.field_pos = ID_AA64PFR0_SVE_SHIFT,
+		.min_field_value = ID_AA64PFR0_SVE,
+		.matches = has_cpuid_feature,
+		.enable = sve_kernel_enable,
+	},
+#endif /* CONFIG_ARM64_SVE */
 	{},
 };
 
···
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_JSCVT_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_JSCVT),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_FCMA_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_FCMA),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_LRCPC_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_LRCPC),
+#ifdef CONFIG_ARM64_SVE
+	HWCAP_CAP(SYS_ID_AA64PFR0_EL1, ID_AA64PFR0_SVE_SHIFT, FTR_UNSIGNED, ID_AA64PFR0_SVE, CAP_HWCAP, HWCAP_SVE),
+#endif
 	{},
 };
 

arch/arm64/kernel/cpuinfo.c

···
 	"sm4",
 	"asimddp",
 	"sha512",
+	"sve",
 	NULL
 };
 

arch/arm64/kernel/entry.S

···
 	mov	wscno, w8			// syscall number in w8
 	mov	wsc_nr, #__NR_syscalls
 
-#ifndef CONFIG_ARM64_SVE
+#ifdef CONFIG_ARM64_SVE
+alternative_if_not ARM64_SVE
 	b	el0_svc_naked
-#else
+alternative_else_nop_endif
 	tbz	x16, #TIF_SVE, el0_svc_naked	// Skip unless TIF_SVE set:
 	bic	x16, x16, #_TIF_SVE		// discard SVE state
 	str	x16, [tsk, #TSK_TI_FLAGS]
···
 	mrs	x9, cpacr_el1
 	bic	x9, x9, #CPACR_EL1_ZEN_EL0EN	// disable SVE for el0
 	msr	cpacr_el1, x9			// synchronised by eret to el0
-#endif /* CONFIG_ARM64_SVE */
+#endif
 
 el0_svc_naked:					// compat entry point
 	stp	x0, xscno, [sp, #S_ORIG_X0]	// save the original x0 and syscall number