KVM: riscv: selftests: Add exception handling support

Add the infrastructure for guest exception handling in riscv selftests.
Customized handlers can be enabled by vm_install_exception_handler(vector)
or vm_install_interrupt_handler().

The code is inspired from that of x86/arm64.

Signed-off-by: Haibo Xu <[e-mail]>
Reviewed-by: Andrew Jones <[e-mail]>
Signed-off-by: Anup Patel <[e-mail]>

tools/testing/selftests/kvm/Makefile

···
 LIBKVM_s390x += lib/s390x/processor.c
 LIBKVM_s390x += lib/s390x/ucall.c
 
+LIBKVM_riscv += lib/riscv/handlers.S
 LIBKVM_riscv += lib/riscv/processor.c
 LIBKVM_riscv += lib/riscv/ucall.c
 

tools/testing/selftests/kvm/include/riscv/processor.h

···
 						     KVM_REG_RISCV_SBI_SINGLE,		\
 						     idx, KVM_REG_SIZE_ULONG)
 
+struct ex_regs {
+	unsigned long ra;
+	unsigned long sp;
+	unsigned long gp;
+	unsigned long tp;
+	unsigned long t0;
+	unsigned long t1;
+	unsigned long t2;
+	unsigned long s0;
+	unsigned long s1;
+	unsigned long a0;
+	unsigned long a1;
+	unsigned long a2;
+	unsigned long a3;
+	unsigned long a4;
+	unsigned long a5;
+	unsigned long a6;
+	unsigned long a7;
+	unsigned long s2;
+	unsigned long s3;
+	unsigned long s4;
+	unsigned long s5;
+	unsigned long s6;
+	unsigned long s7;
+	unsigned long s8;
+	unsigned long s9;
+	unsigned long s10;
+	unsigned long s11;
+	unsigned long t3;
+	unsigned long t4;
+	unsigned long t5;
+	unsigned long t6;
+	unsigned long epc;
+	unsigned long status;
+	unsigned long cause;
+};
+
+#define NR_VECTORS  2
+#define NR_EXCEPTIONS  32
+#define EC_MASK  (NR_EXCEPTIONS - 1)
+
+typedef void(*exception_handler_fn)(struct ex_regs *);
+
+void vm_init_vector_tables(struct kvm_vm *vm);
+void vcpu_init_vector_tables(struct kvm_vcpu *vcpu);
+
+void vm_install_exception_handler(struct kvm_vm *vm, int vector, exception_handler_fn handler);
+
+void vm_install_interrupt_handler(struct kvm_vm *vm, exception_handler_fn handler);
+
 /* L3 index Bit[47:39] */
 #define PGTBL_L3_INDEX_MASK			0x0000FF8000000000ULL
 #define PGTBL_L3_INDEX_SHIFT			39

tools/testing/selftests/kvm/lib/riscv/handlers.S

···
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Intel Corporation
+ */
+
+#ifndef __ASSEMBLY__
+#define __ASSEMBLY__
+#endif
+
+#include <asm/csr.h>
+
+.macro save_context
+	addi  sp, sp, (-8*34)
+	sd    x1, 0(sp)
+	sd    x2, 8(sp)
+	sd    x3, 16(sp)
+	sd    x4, 24(sp)
+	sd    x5, 32(sp)
+	sd    x6, 40(sp)
+	sd    x7, 48(sp)
+	sd    x8, 56(sp)
+	sd    x9, 64(sp)
+	sd    x10, 72(sp)
+	sd    x11, 80(sp)
+	sd    x12, 88(sp)
+	sd    x13, 96(sp)
+	sd    x14, 104(sp)
+	sd    x15, 112(sp)
+	sd    x16, 120(sp)
+	sd    x17, 128(sp)
+	sd    x18, 136(sp)
+	sd    x19, 144(sp)
+	sd    x20, 152(sp)
+	sd    x21, 160(sp)
+	sd    x22, 168(sp)
+	sd    x23, 176(sp)
+	sd    x24, 184(sp)
+	sd    x25, 192(sp)
+	sd    x26, 200(sp)
+	sd    x27, 208(sp)
+	sd    x28, 216(sp)
+	sd    x29, 224(sp)
+	sd    x30, 232(sp)
+	sd    x31, 240(sp)
+	csrr  s0, CSR_SEPC
+	csrr  s1, CSR_SSTATUS
+	csrr  s2, CSR_SCAUSE
+	sd    s0, 248(sp)
+	sd    s1, 256(sp)
+	sd    s2, 264(sp)
+.endm
+
+.macro restore_context
+	ld    s2, 264(sp)
+	ld    s1, 256(sp)
+	ld    s0, 248(sp)
+	csrw  CSR_SCAUSE, s2
+	csrw  CSR_SSTATUS, s1
+	csrw  CSR_SEPC, s0
+	ld    x31, 240(sp)
+	ld    x30, 232(sp)
+	ld    x29, 224(sp)
+	ld    x28, 216(sp)
+	ld    x27, 208(sp)
+	ld    x26, 200(sp)
+	ld    x25, 192(sp)
+	ld    x24, 184(sp)
+	ld    x23, 176(sp)
+	ld    x22, 168(sp)
+	ld    x21, 160(sp)
+	ld    x20, 152(sp)
+	ld    x19, 144(sp)
+	ld    x18, 136(sp)
+	ld    x17, 128(sp)
+	ld    x16, 120(sp)
+	ld    x15, 112(sp)
+	ld    x14, 104(sp)
+	ld    x13, 96(sp)
+	ld    x12, 88(sp)
+	ld    x11, 80(sp)
+	ld    x10, 72(sp)
+	ld    x9, 64(sp)
+	ld    x8, 56(sp)
+	ld    x7, 48(sp)
+	ld    x6, 40(sp)
+	ld    x5, 32(sp)
+	ld    x4, 24(sp)
+	ld    x3, 16(sp)
+	ld    x2, 8(sp)
+	ld    x1, 0(sp)
+	addi  sp, sp, (8*34)
+.endm
+
+.balign 4
+.global exception_vectors
+exception_vectors:
+	save_context
+	move  a0, sp
+	call  route_exception
+	restore_context
+	sret

tools/testing/selftests/kvm/lib/riscv/processor.c

···
 
 #define DEFAULT_RISCV_GUEST_STACK_VADDR_MIN	0xac0000
 
+static vm_vaddr_t exception_handlers;
+
 static uint64_t page_align(struct kvm_vm *vm, uint64_t v)
 {
 	return (v + vm->page_size) & ~(vm->page_size - 1);
···
 	va_end(ap);
 }
 
+void kvm_exit_unexpected_exception(int vector, int ec)
+{
+	ucall(UCALL_UNHANDLED, 2, vector, ec);
+}
+
 void assert_on_unhandled_exception(struct kvm_vcpu *vcpu)
 {
+	struct ucall uc;
+
+	if (get_ucall(vcpu, &uc) == UCALL_UNHANDLED) {
+		TEST_FAIL("Unexpected exception (vector:0x%lx, ec:0x%lx)",
+			uc.args[0], uc.args[1]);
+	}
+}
+
+struct handlers {
+	exception_handler_fn exception_handlers[NR_VECTORS][NR_EXCEPTIONS];
+};
+
+void route_exception(struct ex_regs *regs)
+{
+	struct handlers *handlers = (struct handlers *)exception_handlers;
+	int vector = 0, ec;
+
+	ec = regs->cause & ~CAUSE_IRQ_FLAG;
+	if (ec >= NR_EXCEPTIONS)
+		goto unexpected_exception;
+
+	/* Use the same handler for all the interrupts */
+	if (regs->cause & CAUSE_IRQ_FLAG) {
+		vector = 1;
+		ec = 0;
+	}
+
+	if (handlers && handlers->exception_handlers[vector][ec])
+		return handlers->exception_handlers[vector][ec](regs);
+
+unexpected_exception:
+	return kvm_exit_unexpected_exception(vector, ec);
+}
+
+void vcpu_init_vector_tables(struct kvm_vcpu *vcpu)
+{
+	extern char exception_vectors;
+
+	vcpu_set_reg(vcpu, RISCV_GENERAL_CSR_REG(stvec), (unsigned long)&exception_vectors);
+}
+
+void vm_init_vector_tables(struct kvm_vm *vm)
+{
+	vm->handlers = __vm_vaddr_alloc(vm, sizeof(struct handlers),
+				   vm->page_size, MEM_REGION_DATA);
+
+	*(vm_vaddr_t *)addr_gva2hva(vm, (vm_vaddr_t)(&exception_handlers)) = vm->handlers;
+}
+
+void vm_install_exception_handler(struct kvm_vm *vm, int vector, exception_handler_fn handler)
+{
+	struct handlers *handlers = addr_gva2hva(vm, vm->handlers);
+
+	assert(vector < NR_EXCEPTIONS);
+	handlers->exception_handlers[0][vector] = handler;
+}
+
+void vm_install_interrupt_handler(struct kvm_vm *vm, exception_handler_fn handler)
+{
+	struct handlers *handlers = addr_gva2hva(vm, vm->handlers);
+
+	handlers->exception_handlers[1][0] = handler;
 }
 
 struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0,