Re: [PATCH] target/loongarch/kvm: Fix VM recovery from disk failures

[Philippe Mathieu-Daudé]

(Cc'ing migration maintainers)

On 30/4/24 03:23, Song Gao wrote:
> vmstate does not save kvm_state_conter,
> which can cause VM recovery from disk to fail.

Cc: qemu-stable@nongnu.org
Fixes: d11681c94f ("target/loongarch: Implement kvm_arch_init_vcpu")

> Signed-off-by: Song Gao <gaosong@loongson.cn>
> ---
>   target/loongarch/machine.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/target/loongarch/machine.c b/target/loongarch/machine.c
> index c7029fb9b4..4cd1bf06ff 100644
> --- a/target/loongarch/machine.c
> +++ b/target/loongarch/machine.c
> @@ -191,6 +191,8 @@ const VMStateDescription vmstate_loongarch_cpu = {
>           VMSTATE_STRUCT_ARRAY(env.tlb, LoongArchCPU, LOONGARCH_TLB_MAX,
>                                0, vmstate_tlb, LoongArchTLB),
>   
> +        VMSTATE_UINT64(kvm_state_counter, LoongArchCPU),
> +
>           VMSTATE_END_OF_LIST()
>       },
>       .subsections = (const VMStateDescription * const []) {

The migration stream is versioned, so you should increase it,
but this field is only relevant for KVM (it shouldn't be there
in non-KVM builds). IMHO the correct migration way to fix that
is (untested):

-- >8 --
diff --git a/target/loongarch/machine.c b/target/loongarch/machine.c
index c7029fb9b4..08032c6d71 100644
--- a/target/loongarch/machine.c
+++ b/target/loongarch/machine.c
@@ -8,8 +8,27 @@
 #include "qemu/osdep.h"
 #include "cpu.h"
 #include "migration/cpu.h"
+#include "sysemu/kvm.h"
 #include "vec.h"

+#ifdef CONFIG_KVM
+static bool kvmcpu_needed(void *opaque)
+{
+    return kvm_enabled();
+}
+
+static const VMStateDescription vmstate_kvmtimer = {
+    .name = "cpu/kvmtimer",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = kvmcpu_needed,
+    .fields = (const VMStateField[]) {
+        VMSTATE_UINT64(kvm_state_counter, LoongArchCPU),
+        VMSTATE_END_OF_LIST()
+    }
+};
+#endif /* CONFIG_KVM */
+
 static const VMStateDescription vmstate_fpu_reg = {
     .name = "fpu_reg",
     .version_id = 1,
@@ -194,6 +213,9 @@ const VMStateDescription vmstate_loongarch_cpu = {
         VMSTATE_END_OF_LIST()
     },
     .subsections = (const VMStateDescription * const []) {
+#ifdef CONFIG_KVM
+        &vmstate_kvmcpu,
+#endif
         &vmstate_fpu,
         &vmstate_lsx,
         &vmstate_lasx,
---