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[83.42.66.234]) by smtp.gmail.com with ESMTPSA id d63sm4985317wmd.12.2020.11.17.10.49.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Nov 2020 10:49:38 -0800 (PST) Subject: Re: [PATCH for-5.2] s390x/pci: fix endianness issues To: Thomas Huth , Matthew Rosato , Cornelia Huck References: <20201117171340.1289659-1-cohuck@redhat.com> <4e2cfc7a-9307-6c2a-9237-4ba66eb85ad1@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <17e3595f-6d12-0dc1-2623-d85163c98d3b@redhat.com> Date: Tue, 17 Nov 2020 19:49:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <4e2cfc7a-9307-6c2a-9237-4ba66eb85ad1@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/17 01:18:45 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Pierre Morel , David Hildenbrand , qemu-s390x@nongnu.org, Richard Henderson , qemu-devel@nongnu.org, Halil Pasic , Christian Borntraeger , Alex Williamson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/17/20 7:39 PM, Thomas Huth wrote: > 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 >>>>> --- >>>>> >>>>> 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. I'm confused because the description is about target endianness, but stq_p() is about host alignment. If there is no alignment problem, doesn't using stq_p() make code harder to review?