i386/xen: Implement SCHEDOP_poll and SCHEDOP_yield

They both do the same thing and just call sched_yield. This is enough to
stop the Linux guest panicking when running on a host kernel which doesn't
intercept SCHEDOP_poll and lets it reach userspace.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index 5f2b55ef102dada601b7565da2990300e9bc8e78..80005ea527b98bb41ccd02b14d239bccd11329e2 100644 (file)
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -227,6 +227,18 @@ static bool kvm_xen_hcall_sched_op(struct kvm_xen_exit *exit, X86CPU *cpu,
         err = schedop_shutdown(cs, arg);
         break;
 
+    case SCHEDOP_poll:
+        /*
+         * Linux will panic if this doesn't work. Just yield; it's not
+         * worth overthinking it because wWith event channel handling
+         * in KVM, the kernel will intercept this and it will never
+         * reach QEMU anyway.
+         */
+    case SCHEDOP_yield:
+        sched_yield();
+        err = 0;
+        break;
+
     default:
         return false;
     }