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

[Cornelia Huck]

On Tue, 17 Nov 2020 09:02:37 -0500
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> 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?
> 

I just re-added some st?_p operations in set_pbdev_info and that fixes
at least the crash I was seeing with Phil's patch applied. Still, no
pci functions get detected, so that's not enough. Those memcpy calls
look like a possible culprit.