KVM: selftests: riscv: Add lazy V extension enablement for guests

When the cross-compiler defaults to an -march that includes the V
(vector) extension, -O2 auto-vectorization generates vector instructions
(e.g. vsetvli, vadd.vv) in guest code. Executing such an instruction with
sstatus.VS Off raises EXC_INST_ILLEGAL (scause=2); KVM's hedeleg forwards
it to the guest, but the bare-metal selftest cannot handle it, so all
guest tests fail. A real kernel handles this via
riscv_v_first_use_handler(), which enables V and re-executes the
instruction.

Fix it in processor.c:

1. Delete the now-unused guest_unexp_trap() handler, replaced by the full
   exception vector table.

2. In vm_arch_vcpu_add(), advertise V to KVM via __vcpu_set_reg(V, 1)
   (best-effort, errors ignored on hardware without V) and install the
   full exception vector table instead of a raw stvec handler.

3. In route_exception(), decode the faulting instruction (stval) with
   insn_is_vector() and, when it is a vector instruction while sstatus.VS
   is Off, set VS to Initial and sret to re-execute it, before any
   test-registered handler. Genuinely illegal instructions still reach
   the unexpected-exception path.

4. Make vm_init_vector_tables() idempotent by checking vm->handlers
   before allocating, so tests that call it directly (ebreak_test,
   arch_timer, sbi_pmu_test) do not leak memory.

Tested on a riscv64 host with KVM enabled.

Signed-off-by: jinrui <jinrui@haiwei.tech>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20EA6EE00884FB87+20260813102930.3892251-1-jinrui@haiwei.tech
Signed-off-by: Anup Patel <anup@brainfault.org>

0 files changed, 0 insertions, 0 deletions