Re: [PULL 35/38] spapr: nested: Introduce H_GUEST_[GET|SET]_STATE hcalls.

[Thomas Huth]

On 27/03/2024 06.41, Harsh Prateek Bora wrote:
> On 3/26/24 21:32, Peter Maydell wrote:
> > On Tue, 12 Mar 2024 at 17:11, Nicholas Piggin <npiggin@gmail.com> wrote:
> > > From: Harsh Prateek Bora <harshpb@linux.ibm.com>
> > >
> > > Introduce the nested PAPR hcalls:
> > >      - H_GUEST_GET_STATE which is used to get state of a nested guest or
> > >        a guest VCPU. The value field for each element in the request is
> > >        destination to be updated to reflect current state on success.
> > >      - H_GUEST_SET_STATE which is used to modify the state of a guest or
> > >        a guest VCPU. On success, guest (or its VCPU) state shall be
> > >        updated as per the value field for the requested element(s).
> > >
> > > Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
> > > Signed-off-by: Michael Neuling <mikey@neuling.org>
> > > Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >
> > Hi; Coverity points out a problem with this code (CID 1540008, 1540009):
> >
> >
> >
> > > +static target_ulong h_guest_getset_state(PowerPCCPU *cpu,
> > > +                                         SpaprMachineState *spapr,
> > > +                                         target_ulong *args,
> > > +                                         bool set)
> > > +{
> > > +    target_ulong flags = args[0];
> > > +    target_ulong lpid = args[1];
> > > +    target_ulong vcpuid = args[2];
> > > +    target_ulong buf = args[3];
> > > +    target_ulong buflen = args[4];
> > > +    struct guest_state_request gsr;
> > > +    SpaprMachineStateNestedGuest *guest;
> > > +
> > > +    guest = spapr_get_nested_guest(spapr, lpid);
> > > +    if (!guest) {
> > > +        return H_P2;
> > > +    }
> > > +    gsr.buf = buf;
> > > +    assert(buflen <= GSB_MAX_BUF_SIZE);
> > > +    gsr.len = buflen;
> > > +    gsr.flags = 0;
> > > +    if (flags & H_GUEST_GETSET_STATE_FLAG_GUEST_WIDE) {
> >
> > flags is a target_ulong, which means it might only be 32 bits.
> > But H_GUEST_GETSET_STATE_FLAG_GUEST_WIDE has a bit set in the
> > upper 32 bits only. So Coverity complains about this condition
> > being always-zero and the body of the if being dead code.
> >
> > What was the intention here?
>
> Hi Peter,
> Ideally this is intended to be running on a ppc64 where target_ulong
> should be uint64_t. I guess same holds true for existing nested-hv code
> as well.
>
> Hi Nick,
> Do you think keeping both nested APIs (i.e. entire spapr_nested.c)
> within #ifdef TARGET_PPC64 would be a better choice here?

spapr_numa.c is only included with CONFIG_PSERIES in hw/ppc/meson.build, so 
that should already take care that this code is only compiled with a 64-bit 
target ... Can we somehow teach Coverity to take that into consideration?

 Thomas