RISC-V: KVM: Redirect AMO load/store misaligned traps to guest

The M-mode redirects an unhandled misaligned trap back
to S-mode when not delegating it to VS-mode(hedeleg).
However, KVM running in HS-mode terminates the VS-mode
software when back from M-mode.
The KVM should redirect the trap back to VS-mode, and
let VS-mode trap handler decide the next step.
Here is a way to handle misaligned traps in KVM,
not only directing them to VS-mode or terminate it.

Signed-off-by: wchen <waylingII@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: wayling

arch/riscv/include/asm/csr.h

@@ -82,7 +82,9 @@
 #define EXC_INST_ACCESS		1
 #define EXC_INST_ILLEGAL	2
 #define EXC_BREAKPOINT		3
+#define EXC_LOAD_MISALIGNED	4
 #define EXC_LOAD_ACCESS		5
+#define EXC_STORE_MISALIGNED	6
 #define EXC_STORE_ACCESS	7
 #define EXC_SYSCALL		8
 #define EXC_HYPERVISOR_SYSCALL	9

arch/riscv/kvm/vcpu_exit.c

@@ -183,6 +183,8 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	run->exit_reason = KVM_EXIT_UNKNOWN;
 	switch (trap->scause) {
 	case EXC_INST_ILLEGAL:
+	case EXC_LOAD_MISALIGNED:
+	case EXC_STORE_MISALIGNED:
 		if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV) {
 			kvm_riscv_vcpu_trap_redirect(vcpu, trap);
 			ret = 1;