diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 347805446151..50fa174cccb9 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -26,13 +26,41 @@ struct riscv_isainfo {
 	DECLARE_BITMAP(isa, RISCV_ISA_EXT_MAX);
 };
 
+struct riscv_isavendorinfo {
+	DECLARE_BITMAP(isa, RISCV_ISA_VENDOR_EXT_SIZE);
+};
+
 DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
 
 /* Per-cpu ISA extensions. */
 extern struct riscv_isainfo hart_isa[NR_CPUS];
 
+/* Per-cpu ISA vendor extensions. */
+extern struct riscv_isainfo hart_isa_vendor[NR_CPUS];
+
+/* Vendor that is associated with hart_isa_vendor */
+extern unsigned long hart_isa_vendorid;
+
 void riscv_user_isa_enable(void);
 
+#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size) {	\
+	.name = #_name,								\
+	.property = #_name,							\
+	.id = _id,								\
+	.subset_ext_ids = _subset_exts,						\
+	.subset_ext_size = _subset_exts_size					\
+}
+
+#define __RISCV_ISA_EXT_DATA(_name, _id) _RISCV_ISA_EXT_DATA(_name, _id, NULL, 0)
+
+/* Used to declare pure "lasso" extension (Zk for instance) */
+#define __RISCV_ISA_EXT_BUNDLE(_name, _bundled_exts) \
+	_RISCV_ISA_EXT_DATA(_name, RISCV_ISA_EXT_INVALID, _bundled_exts, ARRAY_SIZE(_bundled_exts))
+
+/* Used to declare extensions that are a superset of other extensions (Zvbb for instance) */
+#define __RISCV_ISA_EXT_SUPERSET(_name, _id, _sub_exts) \
+	_RISCV_ISA_EXT_DATA(_name, _id, _sub_exts, ARRAY_SIZE(_sub_exts))
+
 #if defined(CONFIG_RISCV_MISALIGNED)
 bool check_unaligned_access_emulated_all_cpus(void);
 void unaligned_emulation_finish(void);
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index e17d0078a651..38157be5becd 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -87,6 +87,29 @@
 #define RISCV_ISA_EXT_MAX		128
 #define RISCV_ISA_EXT_INVALID		U32_MAX
 
+/*
+ * These macros represent the logical IDs of each vendor RISC-V ISA extension
+ * and are used in each vendor ISA bitmap. The logical IDs start from
+ * RISCV_ISA_VENDOR_EXT_BASE, which allows the 0-0x7999 range to be
+ * reserved for non-vendor extensions. The maximum, RISCV_ISA_VENDOR_EXT_MAX,
+ * is defined in order to allocate the bitmap and may be increased when
+ * necessary.
+ *
+ * Values are expected to overlap between vendors.
+ *
+ * New extensions should just be added to the bottom of the respective vendor,
+ * rather than added alphabetically, in order to avoid unnecessary shuffling.
+ *
+ */
+#define RISCV_ISA_VENDOR_EXT_BASE		0x8000
+
+/* THead Vendor Extensions */
+#define RISCV_ISA_VENDOR_EXT_XTHEADVECTOR	0x8000
+
+#define RISCV_ISA_VENDOR_EXT_MAX		0x8080
+#define RISCV_ISA_VENDOR_EXT_SIZE		(RISCV_ISA_VENDOR_EXT_MAX - RISCV_ISA_VENDOR_EXT_BASE)
+#define RISCV_ISA_VENDOR_EXT_INVALID		U32_MAX
+
 #ifdef CONFIG_RISCV_M_MODE
 #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SMAIA
 #else
diff --git a/arch/riscv/include/asm/vendor_extensions.h b/arch/riscv/include/asm/vendor_extensions.h
new file mode 100644
index 000000000000..0a1955e1c900
--- /dev/null
+++ b/arch/riscv/include/asm/vendor_extensions.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2024 Rivos, Inc
+ */
+
+#ifndef _ASM_VENDOR_EXTENSIONS_H
+#define _ASM_VENDOR_EXTENSIONS_H
+
+extern const struct riscv_isa_ext_data riscv_isa_vendor_ext_thead[];
+extern const size_t riscv_isa_vendor_ext_count_thead;
+
+bool get_isa_vendor_ext(unsigned long vendorid, const struct riscv_isa_ext_data **isa_vendor_ext,
+			size_t *count);
+
+#endif
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 81d94a8ee10f..53361c50fb46 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -58,6 +58,8 @@ obj-y	+= riscv_ksyms.o
 obj-y	+= stacktrace.o
 obj-y	+= cacheinfo.o
 obj-y	+= patch.o
+obj-y	+= vendor_extensions.o
+obj-y	+= vendor_extensions/
 obj-y	+= probes/
 obj-y	+= tests/
 obj-$(CONFIG_MMU) += vdso.o vdso/
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 6dff7bb1db3f..d7a33e017a15 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -24,6 +24,7 @@
 #include <asm/processor.h>
 #include <asm/sbi.h>
 #include <asm/vector.h>
+#include <asm/vendor_extensions.h>
 
 #define NUM_ALPHA_EXTS ('z' - 'a' + 1)
 
@@ -32,9 +33,18 @@ unsigned long elf_hwcap __read_mostly;
 /* Host ISA bitmap */
 static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 
+/* Host ISA vendor bitmap */
+static DECLARE_BITMAP(riscv_isa_vendor, RISCV_ISA_VENDOR_EXT_SIZE) __read_mostly;
+
 /* Per-cpu ISA extensions. */
 struct riscv_isainfo hart_isa[NR_CPUS];
 
+/* Per-cpu ISA vendor extensions. */
+struct riscv_isainfo hart_isa_vendor[NR_CPUS];
+
+/* Vendor that is associated with hart_isa_vendor */
+unsigned long hart_isa_vendorid;
+
 /**
  * riscv_isa_extension_base() - Get base extension word
  *
@@ -100,24 +110,6 @@ static bool riscv_isa_extension_check(int id)
 	return true;
 }
 
-#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size) {	\
-	.name = #_name,								\
-	.property = #_name,							\
-	.id = _id,								\
-	.subset_ext_ids = _subset_exts,						\
-	.subset_ext_size = _subset_exts_size					\
-}
-
-#define __RISCV_ISA_EXT_DATA(_name, _id) _RISCV_ISA_EXT_DATA(_name, _id, NULL, 0)
-
-/* Used to declare pure "lasso" extension (Zk for instance) */
-#define __RISCV_ISA_EXT_BUNDLE(_name, _bundled_exts) \
-	_RISCV_ISA_EXT_DATA(_name, RISCV_ISA_EXT_INVALID, _bundled_exts, ARRAY_SIZE(_bundled_exts))
-
-/* Used to declare extensions that are a superset of other extensions (Zvbb for instance) */
-#define __RISCV_ISA_EXT_SUPERSET(_name, _id, _sub_exts) \
-	_RISCV_ISA_EXT_DATA(_name, _id, _sub_exts, ARRAY_SIZE(_sub_exts))
-
 static const unsigned int riscv_zk_bundled_exts[] = {
 	RISCV_ISA_EXT_ZBKB,
 	RISCV_ISA_EXT_ZBKC,
@@ -351,6 +343,14 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
 		bool ext_long = false, ext_err = false;
 
 		switch (*ext) {
+		case 'x':
+		case 'X':
+			pr_warn("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.");
+			/*
+			 * In canonical order, the remaining extensions in the
+			 * isa string will be vendor extensions so exit.
+			 */
+			break;
 		case 's':
 			/*
 			 * Workaround for invalid single-letter 's' & 'u' (QEMU).
@@ -366,8 +366,6 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
 			}
 			fallthrough;
 		case 'S':
-		case 'x':
-		case 'X':
 		case 'z':
 		case 'Z':
 			/*
@@ -578,15 +576,54 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
 		acpi_put_table((struct acpi_table_header *)rhct);
 }
 
+static void __init riscv_add_cpu_ext(struct device_node *cpu_node,
+				     unsigned long *this_hwcap,
+				     unsigned long *isa2hwcap,
+				     const struct riscv_isa_ext_data *riscv_isa_ext_data,
+				     struct riscv_isainfo *isainfo,
+				     unsigned int id_offset,
+				     size_t riscv_isa_ext_count)
+{
+	for (int i = 0; i < riscv_isa_ext_count; i++) {
+		const struct riscv_isa_ext_data ext = riscv_isa_ext_data[i];
+
+		if (of_property_match_string(cpu_node, "riscv,isa-extensions",
+					     ext.property) < 0)
+			continue;
+
+		if (ext.subset_ext_size) {
+			for (int j = 0; j < ext.subset_ext_size; j++) {
+				if (riscv_isa_extension_check(ext.subset_ext_ids[j]))
+					set_bit(ext.subset_ext_ids[j] - id_offset, isainfo->isa);
+			}
+		}
+
+		if (riscv_isa_extension_check(ext.id)) {
+			set_bit(ext.id - id_offset, isainfo->isa);
+
+			/* Only single letter extensions get set in hwcap */
+			if (strnlen(ext.name, 2) == 1)
+				*this_hwcap |= isa2hwcap[ext.id];
+		}
+	}
+}
+
 static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
 {
 	unsigned int cpu;
+	u64 boot_vendorid, vendorid;
 
 	for_each_possible_cpu(cpu) {
 		unsigned long this_hwcap = 0;
 		struct device_node *cpu_node;
 		struct riscv_isainfo *isainfo = &hart_isa[cpu];
 
+		struct riscv_isainfo *isavendorinfo = &hart_isa_vendor[cpu];
+		size_t riscv_isa_vendor_ext_count;
+		const struct riscv_isa_ext_data *riscv_isa_vendor_ext;
+		u64 this_vendorid;
+		bool found_vendor;
+
 		cpu_node = of_cpu_device_node_get(cpu);
 		if (!cpu_node) {
 			pr_warn("Unable to find cpu node\n");
@@ -598,28 +635,32 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
 			continue;
 		}
 
-		for (int i = 0; i < riscv_isa_ext_count; i++) {
-			const struct riscv_isa_ext_data *ext = &riscv_isa_ext[i];
+		riscv_add_cpu_ext(cpu_node, &this_hwcap, isa2hwcap,
+				  riscv_isa_ext, isainfo, 0,
+				  riscv_isa_ext_count);
 
-			if (of_property_match_string(cpu_node, "riscv,isa-extensions",
-						     ext->property) < 0)
-				continue;
+		if (of_property_read_u64(cpu_node, "riscv,vendorid", &this_vendorid) < 0) {
+			pr_warn("Unable to find \"riscv,vendorid\" devicetree entry, using boot hart mvendorid instead\n");
+			if (boot_vendorid == -1)
+				boot_vendorid = riscv_get_mvendorid();
+			this_vendorid = boot_vendorid;
+		} else {
+			struct riscv_cpuinfo *ci = per_cpu_ptr(&riscv_cpuinfo, cpu);
 
-			if (ext->subset_ext_size) {
-				for (int j = 0; j < ext->subset_ext_size; j++) {
-					if (riscv_isa_extension_check(ext->subset_ext_ids[j]))
-						set_bit(ext->subset_ext_ids[j], isainfo->isa);
-				}
-			}
+			ci->mvendorid = this_vendorid;
+		}
 
-			if (riscv_isa_extension_check(ext->id)) {
-				set_bit(ext->id, isainfo->isa);
+		found_vendor = get_isa_vendor_ext(this_vendorid,
+						  &riscv_isa_vendor_ext,
+						  &riscv_isa_vendor_ext_count);
 
-				/* Only single letter extensions get set in hwcap */
-				if (strnlen(riscv_isa_ext[i].name, 2) == 1)
-					this_hwcap |= isa2hwcap[riscv_isa_ext[i].id];
-			}
-		}
+		if (found_vendor)
+			riscv_add_cpu_ext(cpu_node, &this_hwcap, isa2hwcap,
+					  riscv_isa_vendor_ext, isavendorinfo,
+					  RISCV_ISA_VENDOR_EXT_BASE, riscv_isa_vendor_ext_count);
+		else
+			pr_warn("No associated vendor extensions with vendor id: %llx\n",
+				vendorid);
 
 		of_node_put(cpu_node);
 
@@ -636,8 +677,27 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
 			bitmap_copy(riscv_isa, isainfo->isa, RISCV_ISA_EXT_MAX);
 		else
 			bitmap_and(riscv_isa, riscv_isa, isainfo->isa, RISCV_ISA_EXT_MAX);
+
+		/*
+		 * All harts must have the same vendorid to have compatible
+		 * vendor extensions.
+		 */
+		if (bitmap_empty(riscv_isa_vendor, RISCV_ISA_VENDOR_EXT_SIZE)) {
+			vendorid = this_vendorid;
+			bitmap_copy(riscv_isa_vendor, isavendorinfo->isa,
+				    RISCV_ISA_VENDOR_EXT_SIZE);
+		} else if (vendorid != this_vendorid) {
+			vendorid = -1ULL;
+			bitmap_clear(riscv_isa_vendor, 0,
+				     RISCV_ISA_VENDOR_EXT_SIZE);
+		} else {
+			bitmap_and(riscv_isa_vendor, riscv_isa_vendor,
+				   isavendorinfo->isa, RISCV_ISA_VENDOR_EXT_SIZE);
+		}
 	}
 
+	hart_isa_vendorid = vendorid;
+
 	if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
 		return -ENOENT;
 
diff --git a/arch/riscv/kernel/vendor_extensions.c b/arch/riscv/kernel/vendor_extensions.c
new file mode 100644
index 000000000000..3a8a6c6dd34e
--- /dev/null
+++ b/arch/riscv/kernel/vendor_extensions.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2024 Rivos, Inc
+ */
+
+#include <asm/cpufeature.h>
+#include <asm/vendorid_list.h>
+#include <asm/vendor_extensions.h>
+
+#include <linux/init.h>
+#include <linux/types.h>
+
+bool __init get_isa_vendor_ext(unsigned long vendorid,
+			       const struct riscv_isa_ext_data **isa_vendor_ext,
+			       size_t *count)
+{
+	bool found_vendor = true;
+
+	switch (vendorid) {
+	case THEAD_VENDOR_ID:
+		*isa_vendor_ext = riscv_isa_vendor_ext_thead;
+		*count = riscv_isa_vendor_ext_count_thead;
+		break;
+	default:
+		*isa_vendor_ext = NULL;
+		*count = 0;
+		found_vendor = false;
+		break;
+	}
+
+	return found_vendor;
+}
diff --git a/arch/riscv/kernel/vendor_extensions/Makefile b/arch/riscv/kernel/vendor_extensions/Makefile
new file mode 100644
index 000000000000..dcf3de8d4658
--- /dev/null
+++ b/arch/riscv/kernel/vendor_extensions/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-y	+= thead_extensions.o
diff --git a/arch/riscv/kernel/vendor_extensions/thead_extensions.c b/arch/riscv/kernel/vendor_extensions/thead_extensions.c
new file mode 100644
index 000000000000..7ac934b1f54c
--- /dev/null
+++ b/arch/riscv/kernel/vendor_extensions/thead_extensions.c
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <asm/cpufeature.h>
+#include <asm/hwcap.h>
+#include <asm/vendor_extensions.h>
+
+#include <linux/array_size.h>
+
+const struct riscv_isa_ext_data riscv_isa_vendor_ext_thead[] = {
+	__RISCV_ISA_EXT_DATA(xtheadvector, RISCV_ISA_VENDOR_EXT_XTHEADVECTOR),
+};
+
+const size_t riscv_isa_vendor_ext_count_thead = ARRAY_SIZE(riscv_isa_vendor_ext_thead);
