[RFC,V4,31/33] target/arm/kvm: Write vCPU's state back to KVM on cold-reset

Commit Message

Salil Mehta Oct. 9, 2024, 3:37 a.m. UTC

From: Jean-Philippe Brucker <[e-mail]>

Previously, all `PSCI_CPU_{ON, OFF}` calls were handled directly by KVM.
However, with the introduction of vCPU hotplug, these hypervisor calls are now
trapped to QEMU for policy checks. This shift can lead to inconsistent vCPU
states between KVM and QEMU, particularly when the vCPU has been recently
plugged in and is transitioning from the unparked state in QOM. Therefore, it is
crucial to synchronize the vCPU state with KVM, especially in the context of a
cold reset of the QOM vCPU.

To ensure this synchronization, mark the QOM vCPU as "dirty" to trigger a call
to `kvm_arch_put_registers()`. This guarantees that KVM’s `MP_STATE` is updated
accordingly, forcing synchronization of the `mp_state` between QEMU and KVM.

Signed-off-by: Jean-Philippe Brucker <[e-mail]>
Signed-off-by: Salil Mehta <[e-mail]>
---
 target/arm/kvm.c | 7 +++++++
 1 file changed, 7 insertions(+)

Patch

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 9a51249a42..a3c98fa213 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -1038,6 +1038,7 @@  void kvm_arm_cpu_post_load(ARMCPU *cpu)
 void kvm_arm_reset_vcpu(ARMCPU *cpu)
 {
     int ret;
+    CPUState *cs = CPU(cpu);
 
     /* Re-init VCPU so that all registers are set to
      * their respective reset values.
@@ -1059,6 +1060,12 @@  void kvm_arm_reset_vcpu(ARMCPU *cpu)
      * for the same reason we do so in kvm_arch_get_registers().
      */
     write_list_to_cpustate(cpu);
+
+    /*
+     * Ensure we call kvm_arch_put_registers(). The vCPU isn't marked dirty if
+     * it was parked in KVM and is now booting from a PSCI CPU_ON call.
+     */
+    cs->vcpu_dirty = true;
 }
 
 void kvm_arm_create_host_vcpu(ARMCPU *cpu)