Re: [RFC PATCH-for-5.2] hw/s390x/pci: Fix endianness issue

[Matthew Rosato]

On 11/17/20 8:31 AM, Cornelia Huck wrote:
> On Tue, 17 Nov 2020 14:23:57 +0100
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
> > On 11/17/20 2:00 PM, Peter Maydell wrote:
> > > On Tue, 17 Nov 2020 at 12:03, Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> > > > Fix an endianness issue reported by Cornelia:
> > > >   
> > > > > s390x tcg guest on x86, virtio-pci devices are not detected. The
> > > > > relevant feature bits are visible to the guest. Same breakage with
> > > > > different guest kernels.
> > > > > KVM guests and s390x tcg guests on s390x are fine.
> > > >
> > > > Fixes: 28dc86a0729 ("s390x/pci: use a PCI Group structure")
> > > > Reported-by: Cornelia Huck <cohuck@redhat.com>
> > > > Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> > > > ---
> > > > RFC because review-only patch, untested
> > > > ---
> > > >    hw/s390x/s390-pci-inst.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
> > > > index 58cd041d17f..cfb54b4d8ec 100644
> > > > --- a/hw/s390x/s390-pci-inst.c
> > > > +++ b/hw/s390x/s390-pci-inst.c
> > > > @@ -305,7 +305,7 @@ int clp_service_call(S390CPU *cpu, uint8_t r2, uintptr_t ra)
> > > >            ClpReqQueryPciGrp *reqgrp = (ClpReqQueryPciGrp *)reqh;
> > > >            S390PCIGroup *group;
> > > >
> > > > -        group = s390_group_find(reqgrp->g);
> > > > +        group = s390_group_find(ldl_p(&reqgrp->g));
> > >
> > > 'g' in the ClpReqQueryPciGrp struct is a uint32_t, so
> > > adding the ldl_p() will have no effect unless (a) the
> > > structure is not 4-aligned and (b) the host will fault on
> > > unaligned accesses, which isn't the case for x86 hosts.
> > >
> > > Q: is this struct really in host order, or should we
> > > be using ldl_le_p() or ldl_be_p() and friends here and
> > > elsewhere?
> > >
> > > thanks
> > > -- PMM
> > >    
> >
> > Hi, I think we better modify the structure here, g should be a byte.
> >
> > Connie, can you please try this if it resolves the issue?
> >
> > diff --git a/hw/s390x/s390-pci-inst.h b/hw/s390x/s390-pci-inst.h
> > index fa3bf8b5aa..641d19c815 100644
> > --- a/hw/s390x/s390-pci-inst.h
> > +++ b/hw/s390x/s390-pci-inst.h
> > @@ -146,7 +146,8 @@ typedef struct ClpReqQueryPciGrp {
> >        uint32_t fmt;
> >        uint64_t reserved1;
> >    #define CLP_REQ_QPCIG_MASK_PFGID 0xff
> > -    uint32_t g;
> > +    uint32_t g0 :24;
> > +    uint32_t g  :8;
> >        uint32_t reserved2;
> >        uint64_t reserved3;
> >    } QEMU_PACKED ClpReqQueryPciGrp;
>
> No, same crash... I fear there are more things broken wrt endianness.

Sorry, just getting online now, looking at the code....  Are the 2 
memcpy calls added in 9670ee75 and 28dc86a0 the issue?  Won't they just 
present the Q PCI FN / Q PCI FN GRP results in host endianness?