Re: [PATCH] ACPI: Avoid infinite recursion when dump-vmstate

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

* Igor Mammedov (imammedo@redhat.com) wrote:
> On Fri, 23 Oct 2020 19:54:41 +0100
> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> 
> > * Igor Mammedov (imammedo@redhat.com) wrote:
> > > On Mon, 19 Oct 2020 17:31:56 +0800
> > > Peng Liang <liangpeng10@huawei.com> wrote:
> > >   
> > > > There is a field with vmstate_ghes_state as vmsd in vmstate_ghes_state,
> > > > which will lead to infinite recursion in dump_vmstate_vmsd.
> > > > 
> > > > Fixes: a08a64627b ("ACPI: Record the Generic Error Status Block address")
> > > > Reported-by: Euler Robot <euler.robot@huawei.com>
> > > > Signed-off-by: Peng Liang <liangpeng10@huawei.com>
> > > > ---
> > > >  hw/acpi/generic_event_device.c | 3 +--
> > > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > > 
> > > > diff --git a/hw/acpi/generic_event_device.c b/hw/acpi/generic_event_device.c
> > > > index 6df400e1ee16..4b6867300a55 100644
> > > > --- a/hw/acpi/generic_event_device.c
> > > > +++ b/hw/acpi/generic_event_device.c
> > > > @@ -334,8 +334,7 @@ static const VMStateDescription vmstate_ghes_state = {
> > > >      .minimum_version_id = 1,
> > > >      .needed = ghes_needed,
> > > >      .fields      = (VMStateField[]) {
> > > > -        VMSTATE_STRUCT(ghes_state, AcpiGedState, 1,
> > > > -                       vmstate_ghes_state, AcpiGhesState),
> > > > +        VMSTATE_UINT64(ghes_state.ghes_addr_le, AcpiGedState),  
> > > 
> > > not sure its' ok handle it this way,
> > > 
> > > see how it is done with another structure:
> > > 
> > > static const VMStateDescription vmstate_ged_state = {                            
> > >     .name = "acpi-ged-state",                                                    
> > >     .version_id = 1,                                                             
> > >     .minimum_version_id = 1,                                                     
> > >     .fields      = (VMStateField[]) {                                            
> > >         VMSTATE_UINT32(sel, GEDState),                                           
> > >         VMSTATE_END_OF_LIST()                                                    
> > >     }                                                                            
> > > }; 
> > > 
> > > ...
> > > 
> > > VMSTATE_STRUCT(ged_state, AcpiGedState, 1, vmstate_ged_state, GEDState),
> > > 
> > > i.e. it looks like we are missing structure definition for AcpiGhesState
> > > 
> > > CCing David,
> > >  to help with migration magic in case I'm wrong or missed something  
> > 
> > Yeh that's confusing :-)
> > 
> > Given a:
> > 
> >   VMSTATE_STRUCT(a, B, 1, vmstate_c, C)
> > 
> > We're saying there's a field 'a' in type B, and field 'a'
> > should be of type C and be serialised using vmstate_c.
> > 
> > That also means that in any vmstate_c, we're expecting it
> > to be passed a type C generally.
> > 
> > Having said that; you don't need a struct - you can get away
> > with that VMSTATE_UINT64, there's two problems:
> > 
> >   a) That assumes that your ghes always stays that simple.
> >   b) If you wanted to store a Ghes from a number of different
> > parent structures then you're stuck because your vmstate_ghes_state
> > is bound to being a strict field of AcpiGedState.
> > 
> > So yes, it's neatest to do it using a VMSD for AcpiGhesState
> > 
> > And congratulations on finding a loop; I don't think we've ever had one
> > before :-)
> 
> can we make compilation fail in case VMSTATE_STRUCT is used but
> is not actually provided like it was in this case?

There's some type checking by the vmstate_offset_value macro; which I
think would have verified that the 'ghes_state' field in AcpiGedState
really is of type AcpiGhesState; but what we don't have is a type
associated with a given VMStateDescription to know what type of state
it's supposed to be called on.

Dave

> > 
> > Dave
> > 
> > > >          VMSTATE_END_OF_LIST()
> > > >      }
> > > >  };  
> > >   
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK