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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

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?

Now than I had lunch, your comment is obvious...

IIUC we should use ldl_le_p() here and fix all the other
uses.

> 
> thanks
> -- PMM
>