LoongArch: KVM: Implement handle csr exception

Implement kvm handle LoongArch vcpu exit caused by reading, writing and
exchanging csr. Use kvm_vcpu_arch::csr structure to emulate the software
registers.
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kvm/exit.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020-2023 Loongson Technology Corporation Limited
+ */
+
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/kvm_host.h>
+#include <linux/module.h>
+#include <linux/preempt.h>
+#include <linux/vmalloc.h>
+#include <asm/fpu.h>
+#include <asm/inst.h>
+#include <asm/loongarch.h>
+#include <asm/mmzone.h>
+#include <asm/numa.h>
+#include <asm/time.h>
+#include <asm/tlb.h>
+#include <asm/kvm_csr.h>
+#include <asm/kvm_vcpu.h>
+#include "trace.h"
+
+static unsigned long kvm_emu_read_csr(struct kvm_vcpu *vcpu, int csrid)
+{
+	unsigned long val = 0;
+	struct loongarch_csrs *csr = vcpu->arch.csr;
+
+	/*
+	 * From LoongArch Reference Manual Volume 1 Chapter 4.2.1
+	 * For undefined CSR id, return value is 0
+	 */
+	if (get_gcsr_flag(csrid) & SW_GCSR)
+		val = kvm_read_sw_gcsr(csr, csrid);
+	else
+		pr_warn_once("Unsupported csrrd 0x%x with pc %lx\n", csrid, vcpu->arch.pc);
+
+	return val;
+}
+
+static unsigned long kvm_emu_write_csr(struct kvm_vcpu *vcpu, int csrid, unsigned long val)
+{
+	unsigned long old = 0;
+	struct loongarch_csrs *csr = vcpu->arch.csr;
+
+	if (get_gcsr_flag(csrid) & SW_GCSR) {
+		old = kvm_read_sw_gcsr(csr, csrid);
+		kvm_write_sw_gcsr(csr, csrid, val);
+	} else
+		pr_warn_once("Unsupported csrwr 0x%x with pc %lx\n", csrid, vcpu->arch.pc);
+
+	return old;
+}
+
+static unsigned long kvm_emu_xchg_csr(struct kvm_vcpu *vcpu, int csrid,
+				unsigned long csr_mask, unsigned long val)
+{
+	unsigned long old = 0;
+	struct loongarch_csrs *csr = vcpu->arch.csr;
+
+	if (get_gcsr_flag(csrid) & SW_GCSR) {
+		old = kvm_read_sw_gcsr(csr, csrid);
+		val = (old & ~csr_mask) | (val & csr_mask);
+		kvm_write_sw_gcsr(csr, csrid, val);
+		old = old & csr_mask;
+	} else
+		pr_warn_once("Unsupported csrxchg 0x%x with pc %lx\n", csrid, vcpu->arch.pc);
+
+	return old;
+}
+
+static int kvm_handle_csr(struct kvm_vcpu *vcpu, larch_inst inst)
+{
+	unsigned int rd, rj, csrid;
+	unsigned long csr_mask, val = 0;
+
+	/*
+	 * CSR value mask imm
+	 * rj = 0 means csrrd
+	 * rj = 1 means csrwr
+	 * rj != 0,1 means csrxchg
+	 */
+	rd = inst.reg2csr_format.rd;
+	rj = inst.reg2csr_format.rj;
+	csrid = inst.reg2csr_format.csr;
+
+	/* Process CSR ops */
+	switch (rj) {
+	case 0: /* process csrrd */
+		val = kvm_emu_read_csr(vcpu, csrid);
+		vcpu->arch.gprs[rd] = val;
+		break;
+	case 1: /* process csrwr */
+		val = vcpu->arch.gprs[rd];
+		val = kvm_emu_write_csr(vcpu, csrid, val);
+		vcpu->arch.gprs[rd] = val;
+		break;
+	default: /* process csrxchg */
+		val = vcpu->arch.gprs[rd];
+		csr_mask = vcpu->arch.gprs[rj];
+		val = kvm_emu_xchg_csr(vcpu, csrid, csr_mask, val);
+		vcpu->arch.gprs[rd] = val;
+	}
+
+	return EMULATE_DONE;
+}