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

[Thomas Huth]

On 17/11/2020 19.30, Philippe Mathieu-Daudé wrote:
> 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?

It's done by the macros. They depend on the target endianess. See cpu-all.h.

 Thomas