diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index 307ceaadbbb9..30686fbb8b9f 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore
@@ -15,6 +15,7 @@
 /x86_64/vmx_preemption_timer_test
 /x86_64/svm_vmcall_test
 /x86_64/sync_regs_test
+/x86_64/userspace_msr_exit_test
 /x86_64/vmx_close_while_nested_test
 /x86_64/vmx_dirty_log_test
 /x86_64/vmx_set_nested_state_test
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index aaaf992faf87..7acc14d06ba8 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -49,6 +49,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/state_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_preemption_timer_test
 TEST_GEN_PROGS_x86_64 += x86_64/svm_vmcall_test
 TEST_GEN_PROGS_x86_64 += x86_64/sync_regs_test
+TEST_GEN_PROGS_x86_64 += x86_64/userspace_msr_exit_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_close_while_nested_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_dirty_log_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index ecbb5e4f9ef6..d5a97401e525 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1595,6 +1595,8 @@ static struct exit_reason {
 	{KVM_EXIT_INTERNAL_ERROR, "INTERNAL_ERROR"},
 	{KVM_EXIT_OSI, "OSI"},
 	{KVM_EXIT_PAPR_HCALL, "PAPR_HCALL"},
+	{KVM_EXIT_X86_RDMSR, "RDMSR"},
+	{KVM_EXIT_X86_WRMSR, "WRMSR"},
 #ifdef KVM_EXIT_MEMORY_NOT_PRESENT
 	{KVM_EXIT_MEMORY_NOT_PRESENT, "MEMORY_NOT_PRESENT"},
 #endif
diff --git a/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c b/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c
new file mode 100644
index 000000000000..e8b6918cdea0
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/userspace_msr_exit_test.c
@@ -0,0 +1,560 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020, Google LLC.
+ *
+ * Tests for exiting into userspace on registered MSRs
+ */
+
+#define _GNU_SOURCE /* for program_invocation_short_name */
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "vmx.h"
+
+/* Forced emulation prefix, used to invoke the emulator unconditionally. */
+#define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
+#define KVM_FEP_LENGTH 5
+static int fep_available = 1;
+
+#define VCPU_ID	      1
+#define MSR_NON_EXISTENT 0x474f4f00
+
+u64 deny_bits = 0;
+struct kvm_msr_filter filter = {
+	.flags = KVM_MSR_FILTER_DEFAULT_ALLOW,
+	.ranges = {
+		{
+			.flags = KVM_MSR_FILTER_READ |
+				 KVM_MSR_FILTER_WRITE,
+			.nmsrs = 1,
+			/* Test an MSR the kernel knows about. */
+			.base = MSR_IA32_XSS,
+			.bitmap = (uint8_t*)&deny_bits,
+		}, {
+			.flags = KVM_MSR_FILTER_READ |
+				 KVM_MSR_FILTER_WRITE,
+			.nmsrs = 1,
+			/* Test an MSR the kernel doesn't know about. */
+			.base = MSR_IA32_FLUSH_CMD,
+			.bitmap = (uint8_t*)&deny_bits,
+		}, {
+			.flags = KVM_MSR_FILTER_READ |
+				 KVM_MSR_FILTER_WRITE,
+			.nmsrs = 1,
+			/* Test a fabricated MSR that no one knows about. */
+			.base = MSR_NON_EXISTENT,
+			.bitmap = (uint8_t*)&deny_bits,
+		},
+	},
+};
+
+struct kvm_msr_filter filter_fs = {
+	.flags = KVM_MSR_FILTER_DEFAULT_ALLOW,
+	.ranges = {
+		{
+			.flags = KVM_MSR_FILTER_READ |
+				 KVM_MSR_FILTER_WRITE,
+			.nmsrs = 1,
+			.base = MSR_FS_BASE,
+			.bitmap = (uint8_t*)&deny_bits,
+		},
+	},
+};
+
+struct kvm_msr_filter filter_gs = {
+	.flags = KVM_MSR_FILTER_DEFAULT_ALLOW,
+	.ranges = {
+		{
+			.flags = KVM_MSR_FILTER_READ |
+				 KVM_MSR_FILTER_WRITE,
+			.nmsrs = 1,
+			.base = MSR_GS_BASE,
+			.bitmap = (uint8_t*)&deny_bits,
+		},
+	},
+};
+
+uint64_t msr_non_existent_data;
+int guest_exception_count;
+
+/*
+ * Note: Force test_rdmsr() to not be inlined to prevent the labels,
+ * rdmsr_start and rdmsr_end, from being defined multiple times.
+ */
+static noinline uint64_t test_rdmsr(uint32_t msr)
+{
+	uint32_t a, d;
+
+	guest_exception_count = 0;
+
+	__asm__ __volatile__("rdmsr_start: rdmsr; rdmsr_end:" :
+			"=a"(a), "=d"(d) : "c"(msr) : "memory");
+
+	return a | ((uint64_t) d << 32);
+}
+
+/*
+ * Note: Force test_wrmsr() to not be inlined to prevent the labels,
+ * wrmsr_start and wrmsr_end, from being defined multiple times.
+ */
+static noinline void test_wrmsr(uint32_t msr, uint64_t value)
+{
+	uint32_t a = value;
+	uint32_t d = value >> 32;
+
+	guest_exception_count = 0;
+
+	__asm__ __volatile__("wrmsr_start: wrmsr; wrmsr_end:" ::
+			"a"(a), "d"(d), "c"(msr) : "memory");
+}
+
+extern char rdmsr_start, rdmsr_end;
+extern char wrmsr_start, wrmsr_end;
+
+/*
+ * Note: Force test_em_rdmsr() to not be inlined to prevent the labels,
+ * rdmsr_start and rdmsr_end, from being defined multiple times.
+ */
+static noinline uint64_t test_em_rdmsr(uint32_t msr)
+{
+	uint32_t a, d;
+
+	guest_exception_count = 0;
+
+	__asm__ __volatile__(KVM_FEP "em_rdmsr_start: rdmsr; em_rdmsr_end:" :
+			"=a"(a), "=d"(d) : "c"(msr) : "memory");
+
+	return a | ((uint64_t) d << 32);
+}
+
+/*
+ * Note: Force test_em_wrmsr() to not be inlined to prevent the labels,
+ * wrmsr_start and wrmsr_end, from being defined multiple times.
+ */
+static noinline void test_em_wrmsr(uint32_t msr, uint64_t value)
+{
+	uint32_t a = value;
+	uint32_t d = value >> 32;
+
+	guest_exception_count = 0;
+
+	__asm__ __volatile__(KVM_FEP "em_wrmsr_start: wrmsr; em_wrmsr_end:" ::
+			"a"(a), "d"(d), "c"(msr) : "memory");
+}
+
+extern char em_rdmsr_start, em_rdmsr_end;
+extern char em_wrmsr_start, em_wrmsr_end;
+
+static void guest_code(void)
+{
+	uint64_t data;
+
+	/*
+	 * Test userspace intercepting rdmsr / wrmsr for MSR_IA32_XSS.
+	 *
+	 * A GP is thrown if anything other than 0 is written to
+	 * MSR_IA32_XSS.
+	 */
+	data = test_rdmsr(MSR_IA32_XSS);
+	GUEST_ASSERT(data == 0);
+	GUEST_ASSERT(guest_exception_count == 0);
+
+	test_wrmsr(MSR_IA32_XSS, 0);
+	GUEST_ASSERT(guest_exception_count == 0);
+
+	test_wrmsr(MSR_IA32_XSS, 1);
+	GUEST_ASSERT(guest_exception_count == 1);
+
+	/*
+	 * Test userspace intercepting rdmsr / wrmsr for MSR_IA32_FLUSH_CMD.
+	 *
+	 * A GP is thrown if MSR_IA32_FLUSH_CMD is read
+	 * from or if a value other than 1 is written to it.
+	 */
+	test_rdmsr(MSR_IA32_FLUSH_CMD);
+	GUEST_ASSERT(guest_exception_count == 1);
+
+	test_wrmsr(MSR_IA32_FLUSH_CMD, 0);
+	GUEST_ASSERT(guest_exception_count == 1);
+
+	test_wrmsr(MSR_IA32_FLUSH_CMD, 1);
+	GUEST_ASSERT(guest_exception_count == 0);
+
+	/*
+	 * Test userspace intercepting rdmsr / wrmsr for MSR_NON_EXISTENT.
+	 *
+	 * Test that a fabricated MSR can pass through the kernel
+	 * and be handled in userspace.
+	 */
+	test_wrmsr(MSR_NON_EXISTENT, 2);
+	GUEST_ASSERT(guest_exception_count == 0);
+
+	data = test_rdmsr(MSR_NON_EXISTENT);
+	GUEST_ASSERT(data == 2);
+	GUEST_ASSERT(guest_exception_count == 0);
+
+	/*
+	 * Test to see if the instruction emulator is available (ie: the module
+	 * parameter 'kvm.force_emulation_prefix=1' is set).  This instruction
+	 * will #UD if it isn't available.
+	 */
+	__asm__ __volatile__(KVM_FEP "nop");
+
+	if (fep_available) {
+		/* Let userspace know we aren't done. */
+		GUEST_SYNC(0);
+
+		/*
+		 * Now run the same tests with the instruction emulator.
+		 */
+		data = test_em_rdmsr(MSR_IA32_XSS);
+		GUEST_ASSERT(data == 0);
+		GUEST_ASSERT(guest_exception_count == 0);
+		test_em_wrmsr(MSR_IA32_XSS, 0);
+		GUEST_ASSERT(guest_exception_count == 0);
+		test_em_wrmsr(MSR_IA32_XSS, 1);
+		GUEST_ASSERT(guest_exception_count == 1);
+
+		test_em_rdmsr(MSR_IA32_FLUSH_CMD);
+		GUEST_ASSERT(guest_exception_count == 1);
+		test_em_wrmsr(MSR_IA32_FLUSH_CMD, 0);
+		GUEST_ASSERT(guest_exception_count == 1);
+		test_em_wrmsr(MSR_IA32_FLUSH_CMD, 1);
+		GUEST_ASSERT(guest_exception_count == 0);
+
+		test_em_wrmsr(MSR_NON_EXISTENT, 2);
+		GUEST_ASSERT(guest_exception_count == 0);
+		data = test_em_rdmsr(MSR_NON_EXISTENT);
+		GUEST_ASSERT(data == 2);
+		GUEST_ASSERT(guest_exception_count == 0);
+	}
+
+	GUEST_DONE();
+}
+
+
+static void guest_code_permission_bitmap(void)
+{
+	uint64_t data;
+
+	test_wrmsr(MSR_FS_BASE, 0);
+	data = test_rdmsr(MSR_FS_BASE);
+	GUEST_ASSERT(data == MSR_FS_BASE);
+
+	test_wrmsr(MSR_GS_BASE, 0);
+	data = test_rdmsr(MSR_GS_BASE);
+	GUEST_ASSERT(data == 0);
+
+	/* Let userspace know to switch the filter */
+	GUEST_SYNC(0);
+
+	test_wrmsr(MSR_FS_BASE, 0);
+	data = test_rdmsr(MSR_FS_BASE);
+	GUEST_ASSERT(data == 0);
+
+	test_wrmsr(MSR_GS_BASE, 0);
+	data = test_rdmsr(MSR_GS_BASE);
+	GUEST_ASSERT(data == MSR_GS_BASE);
+
+	GUEST_DONE();
+}
+
+static void __guest_gp_handler(struct ex_regs *regs,
+			       char *r_start, char *r_end,
+			       char *w_start, char *w_end)
+{
+	if (regs->rip == (uintptr_t)r_start) {
+		regs->rip = (uintptr_t)r_end;
+		regs->rax = 0;
+		regs->rdx = 0;
+	} else if (regs->rip == (uintptr_t)w_start) {
+		regs->rip = (uintptr_t)w_end;
+	} else {
+		GUEST_ASSERT(!"RIP is at an unknown location!");
+	}
+
+	++guest_exception_count;
+}
+
+static void guest_gp_handler(struct ex_regs *regs)
+{
+	__guest_gp_handler(regs, &rdmsr_start, &rdmsr_end,
+			   &wrmsr_start, &wrmsr_end);
+}
+
+static void guest_fep_gp_handler(struct ex_regs *regs)
+{
+	__guest_gp_handler(regs, &em_rdmsr_start, &em_rdmsr_end,
+			   &em_wrmsr_start, &em_wrmsr_end);
+}
+
+static void guest_ud_handler(struct ex_regs *regs)
+{
+	fep_available = 0;
+	regs->rip += KVM_FEP_LENGTH;
+}
+
+static void run_guest(struct kvm_vm *vm)
+{
+	int rc;
+
+	rc = _vcpu_run(vm, VCPU_ID);
+	TEST_ASSERT(rc == 0, "vcpu_run failed: %d\n", rc);
+}
+
+static void check_for_guest_assert(struct kvm_vm *vm)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+	struct ucall uc;
+
+	if (run->exit_reason == KVM_EXIT_IO &&
+		get_ucall(vm, VCPU_ID, &uc) == UCALL_ABORT) {
+			TEST_FAIL("%s at %s:%ld", (const char *)uc.args[0],
+				__FILE__, uc.args[1]);
+	}
+}
+
+static void process_rdmsr(struct kvm_vm *vm, uint32_t msr_index)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+
+	check_for_guest_assert(vm);
+
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_X86_RDMSR,
+		    "Unexpected exit reason: %u (%s),\n",
+		    run->exit_reason,
+		    exit_reason_str(run->exit_reason));
+	TEST_ASSERT(run->msr.index == msr_index,
+			"Unexpected msr (0x%04x), expected 0x%04x",
+			run->msr.index, msr_index);
+
+	switch (run->msr.index) {
+	case MSR_IA32_XSS:
+		run->msr.data = 0;
+		break;
+	case MSR_IA32_FLUSH_CMD:
+		run->msr.error = 1;
+		break;
+	case MSR_NON_EXISTENT:
+		run->msr.data = msr_non_existent_data;
+		break;
+	case MSR_FS_BASE:
+		run->msr.data = MSR_FS_BASE;
+		break;
+	case MSR_GS_BASE:
+		run->msr.data = MSR_GS_BASE;
+		break;
+	default:
+		TEST_ASSERT(false, "Unexpected MSR: 0x%04x", run->msr.index);
+	}
+}
+
+static void process_wrmsr(struct kvm_vm *vm, uint32_t msr_index)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+
+	check_for_guest_assert(vm);
+
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_X86_WRMSR,
+		    "Unexpected exit reason: %u (%s),\n",
+		    run->exit_reason,
+		    exit_reason_str(run->exit_reason));
+	TEST_ASSERT(run->msr.index == msr_index,
+			"Unexpected msr (0x%04x), expected 0x%04x",
+			run->msr.index, msr_index);
+
+	switch (run->msr.index) {
+	case MSR_IA32_XSS:
+		if (run->msr.data != 0)
+			run->msr.error = 1;
+		break;
+	case MSR_IA32_FLUSH_CMD:
+		if (run->msr.data != 1)
+			run->msr.error = 1;
+		break;
+	case MSR_NON_EXISTENT:
+		msr_non_existent_data = run->msr.data;
+		break;
+	case MSR_FS_BASE:
+	case MSR_GS_BASE:
+		break;
+	default:
+		TEST_ASSERT(false, "Unexpected MSR: 0x%04x", run->msr.index);
+	}
+}
+
+static void process_ucall_done(struct kvm_vm *vm)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+	struct ucall uc;
+
+	check_for_guest_assert(vm);
+
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+		    "Unexpected exit reason: %u (%s)",
+		    run->exit_reason,
+		    exit_reason_str(run->exit_reason));
+
+	TEST_ASSERT(get_ucall(vm, VCPU_ID, &uc) == UCALL_DONE,
+		    "Unexpected ucall command: %lu, expected UCALL_DONE (%d)",
+		    uc.cmd, UCALL_DONE);
+}
+
+static uint64_t process_ucall(struct kvm_vm *vm)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+	struct ucall uc = {};
+
+	check_for_guest_assert(vm);
+
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+		    "Unexpected exit reason: %u (%s)",
+		    run->exit_reason,
+		    exit_reason_str(run->exit_reason));
+
+	switch (get_ucall(vm, VCPU_ID, &uc)) {
+	case UCALL_SYNC:
+		break;
+	case UCALL_ABORT:
+		check_for_guest_assert(vm);
+		break;
+	case UCALL_DONE:
+		process_ucall_done(vm);
+		break;
+	default:
+		TEST_ASSERT(false, "Unexpected ucall");
+	}
+
+	return uc.cmd;
+}
+
+static void run_guest_then_process_rdmsr(struct kvm_vm *vm, uint32_t msr_index)
+{
+	run_guest(vm);
+	process_rdmsr(vm, msr_index);
+}
+
+static void run_guest_then_process_wrmsr(struct kvm_vm *vm, uint32_t msr_index)
+{
+	run_guest(vm);
+	process_wrmsr(vm, msr_index);
+}
+
+static uint64_t run_guest_then_process_ucall(struct kvm_vm *vm)
+{
+	run_guest(vm);
+	return process_ucall(vm);
+}
+
+static void run_guest_then_process_ucall_done(struct kvm_vm *vm)
+{
+	run_guest(vm);
+	process_ucall_done(vm);
+}
+
+static void test_msr_filter(void) {
+	struct kvm_enable_cap cap = {
+		.cap = KVM_CAP_X86_USER_SPACE_MSR,
+		.args[0] = KVM_MSR_EXIT_REASON_FILTER,
+	};
+	struct kvm_vm *vm;
+	int rc;
+
+	/* Create VM */
+	vm = vm_create_default(VCPU_ID, 0, guest_code);
+	vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
+
+	rc = kvm_check_cap(KVM_CAP_X86_USER_SPACE_MSR);
+	TEST_ASSERT(rc, "KVM_CAP_X86_USER_SPACE_MSR is available");
+	vm_enable_cap(vm, &cap);
+
+	rc = kvm_check_cap(KVM_CAP_X86_MSR_FILTER);
+	TEST_ASSERT(rc, "KVM_CAP_X86_MSR_FILTER is available");
+
+	vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter);
+
+	vm_init_descriptor_tables(vm);
+	vcpu_init_descriptor_tables(vm, VCPU_ID);
+
+	vm_handle_exception(vm, GP_VECTOR, guest_gp_handler);
+
+	/* Process guest code userspace exits. */
+	run_guest_then_process_rdmsr(vm, MSR_IA32_XSS);
+	run_guest_then_process_wrmsr(vm, MSR_IA32_XSS);
+	run_guest_then_process_wrmsr(vm, MSR_IA32_XSS);
+
+	run_guest_then_process_rdmsr(vm, MSR_IA32_FLUSH_CMD);
+	run_guest_then_process_wrmsr(vm, MSR_IA32_FLUSH_CMD);
+	run_guest_then_process_wrmsr(vm, MSR_IA32_FLUSH_CMD);
+
+	run_guest_then_process_wrmsr(vm, MSR_NON_EXISTENT);
+	run_guest_then_process_rdmsr(vm, MSR_NON_EXISTENT);
+
+	vm_handle_exception(vm, UD_VECTOR, guest_ud_handler);
+	run_guest(vm);
+	vm_handle_exception(vm, UD_VECTOR, NULL);
+
+	if (process_ucall(vm) != UCALL_DONE) {
+		vm_handle_exception(vm, GP_VECTOR, guest_fep_gp_handler);
+
+		/* Process emulated rdmsr and wrmsr instructions. */
+		run_guest_then_process_rdmsr(vm, MSR_IA32_XSS);
+		run_guest_then_process_wrmsr(vm, MSR_IA32_XSS);
+		run_guest_then_process_wrmsr(vm, MSR_IA32_XSS);
+
+		run_guest_then_process_rdmsr(vm, MSR_IA32_FLUSH_CMD);
+		run_guest_then_process_wrmsr(vm, MSR_IA32_FLUSH_CMD);
+		run_guest_then_process_wrmsr(vm, MSR_IA32_FLUSH_CMD);
+
+		run_guest_then_process_wrmsr(vm, MSR_NON_EXISTENT);
+		run_guest_then_process_rdmsr(vm, MSR_NON_EXISTENT);
+
+		/* Confirm the guest completed without issues. */
+		run_guest_then_process_ucall_done(vm);
+	} else {
+		printf("To run the instruction emulated tests set the module parameter 'kvm.force_emulation_prefix=1'\n");
+	}
+
+	kvm_vm_free(vm);
+}
+
+static void test_msr_permission_bitmap(void) {
+	struct kvm_enable_cap cap = {
+		.cap = KVM_CAP_X86_USER_SPACE_MSR,
+		.args[0] = KVM_MSR_EXIT_REASON_FILTER,
+	};
+	struct kvm_vm *vm;
+	int rc;
+
+	/* Create VM */
+	vm = vm_create_default(VCPU_ID, 0, guest_code_permission_bitmap);
+	vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
+
+	rc = kvm_check_cap(KVM_CAP_X86_USER_SPACE_MSR);
+	TEST_ASSERT(rc, "KVM_CAP_X86_USER_SPACE_MSR is available");
+	vm_enable_cap(vm, &cap);
+
+	rc = kvm_check_cap(KVM_CAP_X86_MSR_FILTER);
+	TEST_ASSERT(rc, "KVM_CAP_X86_MSR_FILTER is available");
+
+	vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter_fs);
+	run_guest_then_process_wrmsr(vm, MSR_FS_BASE);
+	run_guest_then_process_rdmsr(vm, MSR_FS_BASE);
+	TEST_ASSERT(run_guest_then_process_ucall(vm) == UCALL_SYNC, "Expected ucall state to be UCALL_SYNC.");
+	vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter_gs);
+	run_guest_then_process_wrmsr(vm, MSR_GS_BASE);
+	run_guest_then_process_rdmsr(vm, MSR_GS_BASE);
+	run_guest_then_process_ucall_done(vm);
+
+	kvm_vm_free(vm);
+}
+
+int main(int argc, char *argv[])
+{
+	test_msr_filter();
+
+	test_msr_permission_bitmap();
+
+	return 0;
+}
