KVM: riscv: Support guest wrs.nto

When a guest traps on wrs.nto, call kvm_vcpu_on_spin() to attempt
to yield to the lock holding VCPU. Also extend the KVM ISA extension
ONE_REG interface to allow KVM userspace to detect and enable the
Zawrs extension for the Guest/VM.
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20240426100820.14762-13-ajones@ventanamicro.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/kvm_host.h

@@ -69,6 +69,7 @@ struct kvm_vcpu_stat {
 	struct kvm_vcpu_stat_generic generic;
 	u64 ecall_exit_stat;
 	u64 wfi_exit_stat;
+	u64 wrs_exit_stat;
 	u64 mmio_exit_user;
 	u64 mmio_exit_kernel;
 	u64 csr_exit_user;

arch/riscv/include/uapi/asm/kvm.h

@@ -167,6 +167,7 @@ enum KVM_RISCV_ISA_EXT_ID {
 	KVM_RISCV_ISA_EXT_ZFA,
 	KVM_RISCV_ISA_EXT_ZTSO,
 	KVM_RISCV_ISA_EXT_ZACAS,
+	KVM_RISCV_ISA_EXT_ZAWRS,
 	KVM_RISCV_ISA_EXT_MAX,
 };
 

arch/riscv/kvm/vcpu.c

@@ -25,6 +25,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
 	KVM_GENERIC_VCPU_STATS(),
 	STATS_DESC_COUNTER(VCPU, ecall_exit_stat),
 	STATS_DESC_COUNTER(VCPU, wfi_exit_stat),
+	STATS_DESC_COUNTER(VCPU, wrs_exit_stat),
 	STATS_DESC_COUNTER(VCPU, mmio_exit_user),
 	STATS_DESC_COUNTER(VCPU, mmio_exit_kernel),
 	STATS_DESC_COUNTER(VCPU, csr_exit_user),

arch/riscv/kvm/vcpu_insn.c

@@ -16,6 +16,9 @@
 #define INSN_MASK_WFI		0xffffffff
 #define INSN_MATCH_WFI		0x10500073
 
+#define INSN_MASK_WRS		0xffffffff
+#define INSN_MATCH_WRS		0x00d00073
+
 #define INSN_MATCH_CSRRW	0x1073
 #define INSN_MASK_CSRRW		0x707f
 #define INSN_MATCH_CSRRS	0x2073
@@ -203,6 +206,13 @@ static int wfi_insn(struct kvm_vcpu *vcpu, struct kvm_run *run, ulong insn)
 	return KVM_INSN_CONTINUE_NEXT_SEPC;
 }
 
+static int wrs_insn(struct kvm_vcpu *vcpu, struct kvm_run *run, ulong insn)
+{
+	vcpu->stat.wrs_exit_stat++;
+	kvm_vcpu_on_spin(vcpu, vcpu->arch.guest_context.sstatus & SR_SPP);
+	return KVM_INSN_CONTINUE_NEXT_SEPC;
+}
+
 struct csr_func {
 	unsigned int base;
 	unsigned int count;
@@ -378,6 +388,11 @@ static const struct insn_func system_opcode_funcs[] = {
 		.match = INSN_MATCH_WFI,
 		.func  = wfi_insn,
 	},
+	{
+		.mask  = INSN_MASK_WRS,
+		.match = INSN_MATCH_WRS,
+		.func  = wrs_insn,
+	},
 };
 
 static int system_opcode_insn(struct kvm_vcpu *vcpu, struct kvm_run *run,

arch/riscv/kvm/vcpu_onereg.c

@@ -41,6 +41,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
 	KVM_ISA_EXT_ARR(SVNAPOT),
 	KVM_ISA_EXT_ARR(SVPBMT),
 	KVM_ISA_EXT_ARR(ZACAS),
+	KVM_ISA_EXT_ARR(ZAWRS),
 	KVM_ISA_EXT_ARR(ZBA),
 	KVM_ISA_EXT_ARR(ZBB),
 	KVM_ISA_EXT_ARR(ZBC),
@@ -120,6 +121,7 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
 	case KVM_RISCV_ISA_EXT_SVINVAL:
 	case KVM_RISCV_ISA_EXT_SVNAPOT:
 	case KVM_RISCV_ISA_EXT_ZACAS:
+	case KVM_RISCV_ISA_EXT_ZAWRS:
 	case KVM_RISCV_ISA_EXT_ZBA:
 	case KVM_RISCV_ISA_EXT_ZBB:
 	case KVM_RISCV_ISA_EXT_ZBC: