target/ppc: fix 'skip KVM' cond in cpu_interrupt_exittb()

cpu_interrupt_exittb() was introduced by commit 044897ef4a
("target/ppc: Fix system lockups caused by interrupt_request state
corruption") as a way to wrap cpu_interrupt() helper in BQL.

After that, commit 6d38666a89 ("ppc: Ignore the CPU_INTERRUPT_EXITTB
interrupt with KVM") added a condition to skip this interrupt if we're
running with KVM.

Problem is that the change made by the above commit, testing for
!kvm_enabled() at the start of cpu_interrupt_exittb():

static inline void cpu_interrupt_exittb(CPUState *cs)
{
    if (!kvm_enabled()) {
        return;
    }
    (... do cpu_interrupt(cs, CPU_INTERRUPT_EXITTB) ...)

is doing the opposite of what it intended to do. This will return
immediately if not kvm_enabled(), i.e. it's a emulated CPU, and if
kvm_enabled() it will proceed to fire CPU_INTERRUPT_EXITTB.

Fix the 'skip KVM' condition so the function is a no-op when
kvm_enabled().

CC: Greg Kurz <groug@kaod.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/809
Fixes: 6d38666a89 ("ppc: Ignore the CPU_INTERRUPT_EXITTB interrupt with KVM")
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <20220121160841.9102-1-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

target/ppc/helper_regs.c

@@ -201,7 +201,11 @@ void cpu_get_tb_cpu_state(CPUPPCState *env, target_ulong *pc,
 
 void cpu_interrupt_exittb(CPUState *cs)
 {
-    if (!kvm_enabled()) {
+    /*
+     * We don't need to worry about translation blocks
+     * when running with KVM.
+     */
+    if (kvm_enabled()) {
         return;
     }