Re: [Qemu-devel] [RFC PATCH 1/2] target-ppc: migrate interrupt vectors address for spapr VM

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Mar 21, 2016 at 05:51:22PM +0100, Cédric Le Goater wrote:
> On 03/21/2016 05:18 PM, Thomas Huth wrote:
> > On 21.03.2016 15:02, Cédric Le Goater wrote:
> >> This address is changed by the linux kernel using the H_SET_MODE hcall
> >> and needs to be migrated in order to restart a spapr VM running in
> >> TCG. Other platforms should not be affected.
> >>
> >> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
> >> ---
> >>  target-ppc/machine.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
> >> index 692121e98319..a418d463db83 100644
> >> --- a/target-ppc/machine.c
> >> +++ b/target-ppc/machine.c
> >> @@ -553,6 +553,9 @@ const VMStateDescription vmstate_ppc_cpu = {
> >>          VMSTATE_UINTTL(env.hflags_nmsr, PowerPCCPU),
> >>          /* FIXME: access_type? */
> >>  
> >> +        /* Effective Address of interrupt vectors */
> >> +        VMSTATE_UINTTL(env.excp_prefix, PowerPCCPU),
> >> +
> >>          /* Sanity checking */
> >>          VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
> >>          VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> > 
> > I'm really no expert with all this migration stuff, but don't you have
> > to bump the version_id when you add new fields to the vmstate?
> > ... and/or use VMSTATE_UINTTL_V() so that migration from older versions
> > of QEMU to the current one also still works with KVM? For example, is it
> > still possible to migrate from QEMU 2.5 to QEMU 2.6 in KVM if you only
> > use VMSTATE_UINTTL without the _V suffix?
> 
> Yes. You are right. I think we need something like below.
> 
> Thanks,
> 
> C.
> 
> 
> target-ppc: migrate interrupt vectors address for spapr VM
> 
> This address is changed by the linux kernel using the H_SET_MODE hcall
> and needs to be migrated in order to restart a spapr VM running in
> TCG. Other platforms should not be affected.
> 
> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
> ---
>  target-ppc/machine.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> Index: qemu-dgibson-for-2.6.git/target-ppc/machine.c
> ===================================================================
> --- qemu-dgibson-for-2.6.git.orig/target-ppc/machine.c
> +++ qemu-dgibson-for-2.6.git/target-ppc/machine.c
> @@ -522,7 +522,7 @@ static const VMStateDescription vmstate_
>  
>  const VMStateDescription vmstate_ppc_cpu = {
>      .name = "cpu",
> -    .version_id = 5,
> +    .version_id = 6,
>      .minimum_version_id = 5,
>      .minimum_version_id_old = 4,
>      .load_state_old = cpu_load_old,
> @@ -553,6 +553,9 @@ const VMStateDescription vmstate_ppc_cpu
>          VMSTATE_UINTTL(env.hflags_nmsr, PowerPCCPU),
>          /* FIXME: access_type? */
>  
> +        /* Effective Address of interrupt vectors */
> +        VMSTATE_UINTTL_V(env.excp_prefix, PowerPCCPU, 6),


So, I dislike putting what's essentially emulator internal state (as
opposed to architected state) into the migration stream if we can
possibly avoid it.

I think recalculating excp_prefix from the MSR on incoming migration
is the correct approach here - I see that there are bugs with that in
the other patch, but so far I'm not seeing a reason to migrate
excp_prefix itself.

>          /* Sanity checking */
>          VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
>          VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
> 
> 
>  
> >  Thomas
> > 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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