Re: [Qemu-devel] pseries-2.6 migration from QEMU-2.6 to QEMU-2.7 broken

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Nikunj A Dadhania (nikunj@linux.vnet.ibm.com) wrote:
> Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:
> 
> > On Thu, 2016-09-22 at 14:34 +0530, Nikunj A Dadhania wrote:
> >> Something like this works for KVM:
> >> 
> >> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> >> index 4820f22..1cf3779 100644
> >> --- a/target-ppc/machine.c
> >> +++ b/target-ppc/machine.c
> >> @@ -563,8 +563,8 @@ const VMStateDescription vmstate_ppc_cpu = {
> >>  
> >>          /* Sanity checking */
> >>          VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
> >> -        VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> >> -        VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU),
> >> +        VMSTATE_UNUSED(sizeof(target_ulong)), /* was _EQUAL(env.insns_flags) */
> >> +        VMSTATE_UNUSED(sizeof(target_ulong)), /* was _EQUAL(env.insns_flags2) */
> >>          VMSTATE_UINT32_EQUAL(env.nb_BATs, PowerPCCPU),
> >>          VMSTATE_END_OF_LIST()
> >>      },
> >> 
> >> TCG migration still remains broken with this.
> >
> > Can we have conditionally present flags and a post-load that does some
> > matching ?
> 
> I think its possible like this:
> 
> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> index 4820f22..dc4704e 100644
> --- a/target-ppc/machine.c
> +++ b/target-ppc/machine.c
> @@ -528,6 +528,42 @@ static const VMStateDescription vmstate_tlbmas = {
>      }
>  };
>  
> +static bool ppc_kvm_enabled(void *opaque, int version_id)
> +{
> +    printf("%s: is kvm enabled %d\n", __func__, kvm_enabled());
> +    return !kvm_enabled();
> +}
> +
> +static int get_insns_equal(QEMUFile *f, void *pv, size_t size)
> +{
> +    uint64_t *v = pv;
> +    uint64_t v2;
> +    qemu_get_be64s(f, &v2);
> +
> +    printf("%s: \n", __func__);
> +
> +    if (*v == v2) {
> +        return 0;
> +    }
> +    printf("Did not match, ignore %" PRIu64 " != %" PRIu64 "\n", *v, v2);
> +    return 0;
> +}
> +
> +static void put_insns(QEMUFile *f, void *pv, size_t size)
> +{
> +    uint64_t *v = pv;
> +    qemu_put_be64s(f, v);
> +}
> +
> +const VMStateInfo vmstate_info_insns_equal = {
> +    .name = "insns equal",
> +    .get  = get_insns_equal,
> +    .put  = put_insns,
> +};
> +

I'd prefer it if you can avoid adding qemu_get/put's unless
really desperate; I'm trying to squash all the read/writing back into
standard macros; but I understand it can be tricky.

I'd agree that a post_load is the nicest way; it can return
an error value.
(Oh and ideally use error_report)

Dave

> +#define VMSTATE_INSNS_EQUAL(_f, _s, _t)                                 \
> +    VMSTATE_SINGLE_TEST(_f, _s, _t, 0, vmstate_info_insns_equal, uint64_t)
> +
>  const VMStateDescription vmstate_ppc_cpu = {
>      .name = "cpu",
>      .version_id = 5,
> @@ -563,8 +599,8 @@ const VMStateDescription vmstate_ppc_cpu = {
>  
>          /* Sanity checking */
>          VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
> -        VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> -        VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU),
> +        VMSTATE_INSNS_EQUAL(env.insns_flags, PowerPCCPU, ppc_kvm_enabled),
> +        VMSTATE_INSNS_EQUAL(env.insns_flags2, PowerPCCPU, ppc_kvm_enabled),
>          VMSTATE_UINT32_EQUAL(env.nb_BATs, PowerPCCPU),
>          VMSTATE_END_OF_LIST()
>      },
> 
> 
> TCG migration succeeds and proceeds ahead. But fails somewhere ahead in
> powerpc exception handler:
> 
> [qemu]$ ./ppc64-softmmu/qemu-system-ppc64  -machine pseries-2.6,usb=off -vga none -nographic -m 2G   ../../imgs/guest.disk -monitor pty --incoming tcp:localhost:4444 
> char device redirected to /dev/pts/5 (label compat_monitor0)
> ppc_kvm_enabled: is kvm enabled 0
> get_insns_equal: 
> Did not match, ignore 9223477658187168481 != 9223477658187151905
> ppc_kvm_enabled: is kvm enabled 0
> get_insns_equal: 
> Did not match, ignore 331702 != 69558
> Cannot open font file True
> Cannot open font file True
> qemu: fatal: Trying to deliver HV exception 4 with no HV support
> 
> NIP c0000000000795c8   LR d00000000074407c CTR c000000000079544 XER 0000000000000000 CPU#0
> MSR 8000000000009032 HID0 0000000000000000  HF 8000000000000030 iidx 1 didx 1
> TB 00000007 32202510341 DECR 00596259
> 
> Regards,
> Nikunj
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK