Re: [PATCH for-5.2] s390x/pci: fix endianness issues

[Philippe Mathieu-Daudé]

On 11/17/20 7:19 PM, Matthew Rosato wrote:
> On 11/17/20 12:59 PM, Philippe Mathieu-Daudé wrote:
>> On 11/17/20 6:13 PM, Cornelia Huck wrote:
>>> zPCI control blocks are big endian, we need to take care that we
>>> do proper accesses in order not to break tcg guests on little endian
>>> hosts.
>>>
>>> Fixes: 28dc86a07299 ("s390x/pci: use a PCI Group structure")
>>> Fixes: 9670ee752727 ("s390x/pci: use a PCI Function structure")
>>> Fixes: 1e7552ff5c34 ("s390x/pci: get zPCI function info from host")
>>> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
>>> ---
>>>
>>> Works for me with virtio-pci devices for tcg on x86 and s390x, and
>>> for kvm.
>>> The vfio changes are not strictly needed; did not test them due to
>>> lack of
>>> hardware -- testing appreciated. >>
>>> As this fixes a regression, I want this in 5.2.
>>>
>>> ---
>>>   hw/s390x/s390-pci-bus.c  | 12 ++++++------
>>>   hw/s390x/s390-pci-inst.c |  4 ++--
>>>   hw/s390x/s390-pci-vfio.c |  8 ++++----
>>>   3 files changed, 12 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
>>> index e0dc20ce4a56..17e64e0b1200 100644
>>> --- a/hw/s390x/s390-pci-bus.c
>>> +++ b/hw/s390x/s390-pci-bus.c
>>> @@ -787,12 +787,12 @@ static void s390_pci_init_default_group(void)
>>>     static void set_pbdev_info(S390PCIBusDevice *pbdev)
>>>   {
>>> -    pbdev->zpci_fn.sdma = ZPCI_SDMA_ADDR;
>>> -    pbdev->zpci_fn.edma = ZPCI_EDMA_ADDR;
>>> -    pbdev->zpci_fn.pchid = 0;
>>> +    stq_p(&pbdev->zpci_fn.sdma, ZPCI_SDMA_ADDR);
>>
>> "zPCI control blocks are big endian" so don't we
>> need the _be_ accessors? stq_be_p() etc...
>>
> 
> I don't think this is necessary.  This is only available for target
> s390x, which is always big endian...  cpu-all.h should define stq_p as
> stq_be_p for example inside the #if defined(TARGET_WORDS_BIGENDIAN).

But if you run on little-endian host, you need to byte-swap that,
isn't it?