[Qemu-devel] [PATCH] spapr: reset @kvm_vcpu_dirty before starting CPU

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Normally QEMU kvm_arch_get_registers() reads registers and sets a dirty
flag which prevents further registers reading from KVM till
kvm_arch_put_registers() executes and resets the flag.

However if we run QEMU with "-S" ("suspended"), then execute "info cpus"
from the QEMU monitor, we end up with not reading registers in
rtas_start_cpu() as qmp_query_cpus() calls kvm_cpu_synchronize_state()
which leaves @kvm_vcpu_dirty=true what prevents kvm_cpu_synchronize_state()
from synchronizing registers and we loose the values.

This resets @kvm_vcpu_dirty flag as we do not have content which we really want to
keep at this point as the CPU is halted.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---

We could also reset @kvm_vcpu_dirty in qmp_query_cpus() but that would be
racy.
---
 hw/ppc/spapr_rtas.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 1cb276d..3dade5e 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -185,6 +185,8 @@ static void rtas_start_cpu(PowerPCCPU *cpu_, sPAPREnvironment *spapr,
         /* This will make sure qemu state is up to date with kvm, and
          * mark it dirty so our changes get flushed back before the
          * new cpu enters */
+
+        cs->kvm_vcpu_dirty = false;
         kvm_cpu_synchronize_state(cs);
 
         env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
-- 
1.8.4.rc4