RISC-V: add vector extension validation checks

Using Clement's new validation callbacks, support checking that
dependencies have been satisfied for the vector extensions. From the
kernel's perfective, it's not required to differentiate between the
conditions for all the various vector subsets - it's the firmware's job
to not report impossible combinations. Instead, the kernel only has to
check that the correct config options are enabled and to enforce its
requirement of the d extension being present for FPU support.

Since vector will now be disabled proactively, there's no need to clear
the bit in elf_hwcap in riscv_fill_hwcap() any longer.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250312-eclair-affluent-55b098c3602b@spud
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Author: ConchuOD

arch/riscv/include/asm/cpufeature.h

@@ -56,6 +56,9 @@ void __init riscv_user_isa_enable(void);
 #define __RISCV_ISA_EXT_BUNDLE(_name, _bundled_exts) \
 	_RISCV_ISA_EXT_DATA(_name, RISCV_ISA_EXT_INVALID, _bundled_exts, \
 			    ARRAY_SIZE(_bundled_exts), NULL)
+#define __RISCV_ISA_EXT_BUNDLE_VALIDATE(_name, _bundled_exts, _validate) \
+	_RISCV_ISA_EXT_DATA(_name, RISCV_ISA_EXT_INVALID, _bundled_exts, \
+			    ARRAY_SIZE(_bundled_exts), _validate)
 
 /* Used to declare extensions that are a superset of other extensions (Zvbb for instance) */
 #define __RISCV_ISA_EXT_SUPERSET(_name, _id, _sub_exts) \

arch/riscv/kernel/cpufeature.c

@@ -109,6 +109,38 @@ static int riscv_ext_zicboz_validate(const struct riscv_isa_ext_data *data,
 	return 0;
 }
 
+static int riscv_ext_vector_x_validate(const struct riscv_isa_ext_data *data,
+				       const unsigned long *isa_bitmap)
+{
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_V))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int riscv_ext_vector_float_validate(const struct riscv_isa_ext_data *data,
+					   const unsigned long *isa_bitmap)
+{
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_V))
+		return -EINVAL;
+
+	if (!IS_ENABLED(CONFIG_FPU))
+		return -EINVAL;
+
+	/*
+	 * The kernel doesn't support systems that don't implement both of
+	 * F and D, so if any of the vector extensions that do floating point
+	 * are to be usable, both floating point extensions need to be usable.
+	 *
+	 * Since this function validates vector only, and v/Zve* are probed
+	 * after f/d, there's no need for a deferral here.
+	 */
+	if (!__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_d))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int riscv_ext_zca_depends(const struct riscv_isa_ext_data *data,
 				 const unsigned long *isa_bitmap)
 {
@@ -326,12 +358,10 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_DATA(d, RISCV_ISA_EXT_d),
 	__RISCV_ISA_EXT_DATA(q, RISCV_ISA_EXT_q),
 	__RISCV_ISA_EXT_SUPERSET(c, RISCV_ISA_EXT_c, riscv_c_exts),
-	__RISCV_ISA_EXT_SUPERSET(v, RISCV_ISA_EXT_v, riscv_v_exts),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(v, RISCV_ISA_EXT_v, riscv_v_exts, riscv_ext_vector_float_validate),
 	__RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
-	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicbom, RISCV_ISA_EXT_ZICBOM, riscv_xlinuxenvcfg_exts,
-					  riscv_ext_zicbom_validate),
-	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts,
-					  riscv_ext_zicboz_validate),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicbom, RISCV_ISA_EXT_ZICBOM, riscv_xlinuxenvcfg_exts, riscv_ext_zicbom_validate),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts, riscv_ext_zicboz_validate),
 	__RISCV_ISA_EXT_DATA(ziccrse, RISCV_ISA_EXT_ZICCRSE),
 	__RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
 	__RISCV_ISA_EXT_DATA(zicond, RISCV_ISA_EXT_ZICOND),
@@ -372,11 +402,11 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_DATA(ztso, RISCV_ISA_EXT_ZTSO),
 	__RISCV_ISA_EXT_SUPERSET(zvbb, RISCV_ISA_EXT_ZVBB, riscv_zvbb_exts),
 	__RISCV_ISA_EXT_DATA(zvbc, RISCV_ISA_EXT_ZVBC),
-	__RISCV_ISA_EXT_SUPERSET(zve32f, RISCV_ISA_EXT_ZVE32F, riscv_zve32f_exts),
-	__RISCV_ISA_EXT_DATA(zve32x, RISCV_ISA_EXT_ZVE32X),
-	__RISCV_ISA_EXT_SUPERSET(zve64d, RISCV_ISA_EXT_ZVE64D, riscv_zve64d_exts),
-	__RISCV_ISA_EXT_SUPERSET(zve64f, RISCV_ISA_EXT_ZVE64F, riscv_zve64f_exts),
-	__RISCV_ISA_EXT_SUPERSET(zve64x, RISCV_ISA_EXT_ZVE64X, riscv_zve64x_exts),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zve32f, RISCV_ISA_EXT_ZVE32F, riscv_zve32f_exts, riscv_ext_vector_float_validate),
+	__RISCV_ISA_EXT_DATA_VALIDATE(zve32x, RISCV_ISA_EXT_ZVE32X, riscv_ext_vector_x_validate),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zve64d, RISCV_ISA_EXT_ZVE64D, riscv_zve64d_exts, riscv_ext_vector_float_validate),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zve64f, RISCV_ISA_EXT_ZVE64F, riscv_zve64f_exts, riscv_ext_vector_float_validate),
+	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zve64x, RISCV_ISA_EXT_ZVE64X, riscv_zve64x_exts, riscv_ext_vector_x_validate),
 	__RISCV_ISA_EXT_DATA(zvfh, RISCV_ISA_EXT_ZVFH),
 	__RISCV_ISA_EXT_DATA(zvfhmin, RISCV_ISA_EXT_ZVFHMIN),
 	__RISCV_ISA_EXT_DATA(zvkb, RISCV_ISA_EXT_ZVKB),
@@ -960,16 +990,6 @@ void __init riscv_fill_hwcap(void)
 		riscv_v_setup_vsize();
 	}
 
-	if (elf_hwcap & COMPAT_HWCAP_ISA_V) {
-		/*
-		 * ISA string in device tree might have 'v' flag, but
-		 * CONFIG_RISCV_ISA_V is disabled in kernel.
-		 * Clear V flag in elf_hwcap if CONFIG_RISCV_ISA_V is disabled.
-		 */
-		if (!IS_ENABLED(CONFIG_RISCV_ISA_V))
-			elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
-	}
-
 	memset(print_str, 0, sizeof(print_str));
 	for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
 		if (riscv_isa[0] & BIT_MASK(i))