RISC-V: KVM: Add extensible CSR emulation framework

We add an extensible CSR emulation framework which is based upon the
existing system instruction emulation. This will be useful to upcoming
AIA, PMU, Nested and other virtualization features.

The CSR emulation framework also has provision to emulate CSR in user
space but this will be used only in very specific cases such as AIA
IMSIC CSR emulation in user space or vendor specific CSR emulation
in user space.

By default, all CSRs not handled by KVM RISC-V will be redirected back
to Guest VCPU as illegal instruction trap.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

2 files changed, 11 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index d482d771eba4..59a0cf2ca7b9 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -65,6 +65,8 @@ struct kvm_vcpu_stat {
 	u64 wfi_exit_stat;
 	u64 mmio_exit_user;
 	u64 mmio_exit_kernel;
+	u64 csr_exit_user;
+	u64 csr_exit_kernel;
 	u64 exits;
 };
 
@@ -210,6 +212,9 @@ struct kvm_vcpu_arch {
 	/* MMIO instruction details */
 	struct kvm_mmio_decode mmio_decode;
 
+	/* CSR instruction details */
+	struct kvm_csr_decode csr_decode;
+
 	/* SBI context */
 	struct kvm_sbi_context sbi_context;
 
diff --git a/arch/riscv/include/asm/kvm_vcpu_insn.h b/arch/riscv/include/asm/kvm_vcpu_insn.h
index 3351eb61a251..350011c83581 100644
--- a/arch/riscv/include/asm/kvm_vcpu_insn.h
+++ b/arch/riscv/include/asm/kvm_vcpu_insn.h
@@ -18,6 +18,11 @@ struct kvm_mmio_decode {
 	int return_handled;
 };
 
+struct kvm_csr_decode {
+	unsigned long insn;
+	int return_handled;
+};
+
 /* Return values used by function emulating a particular instruction */
 enum kvm_insn_return {
 	KVM_INSN_EXIT_TO_USER_SPACE = 0,
@@ -28,6 +33,7 @@ enum kvm_insn_return {
 };
 
 void kvm_riscv_vcpu_wfi(struct kvm_vcpu *vcpu);
+int kvm_riscv_vcpu_csr_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
 int kvm_riscv_vcpu_virtual_insn(struct kvm_vcpu *vcpu, struct kvm_run *run,
 				struct kvm_cpu_trap *trap);