RISC-V: KVM: Forward SEED CSR access to user space

The SEED CSR access from VS/VU mode (guest) will always trap to
HS-mode (KVM) when Zkr extension is available to the Guest/VM.

Forward this CSR access to KVM user space so that it can be
emulated based on the method chosen by VMM.

Fixes: f370b4e6 ("RISC-V: KVM: Allow scalar crypto extensions for Guest/VM")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/vcpu_insn.c

@@ -7,6 +7,8 @@
 #include <linux/bitops.h>
 #include <linux/kvm_host.h>
 
+#include <asm/cpufeature.h>
+
 #define INSN_OPCODE_MASK	0x007c
 #define INSN_OPCODE_SHIFT	2
 #define INSN_OPCODE_SYSTEM	28
@@ -213,9 +215,20 @@ struct csr_func {
 		    unsigned long wr_mask);
 };
 
+static int seed_csr_rmw(struct kvm_vcpu *vcpu, unsigned int csr_num,
+			unsigned long *val, unsigned long new_val,
+			unsigned long wr_mask)
+{
+	if (!riscv_isa_extension_available(vcpu->arch.isa, ZKR))
+		return KVM_INSN_ILLEGAL_TRAP;
+
+	return KVM_INSN_EXIT_TO_USER_SPACE;
+}
+
 static const struct csr_func csr_funcs[] = {
 	KVM_RISCV_VCPU_AIA_CSR_FUNCS
 	KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS
+	{ .base = CSR_SEED, .count = 1, .func = seed_csr_rmw },
 };
 
 /**