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[83.42.66.234]) by smtp.gmail.com with ESMTPSA id b1sm2954583wmd.43.2020.11.05.05.53.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Nov 2020 05:53:18 -0800 (PST) Subject: Re: [PATCH-for-6.0 1/3] hw/virtio: Add configure switch to disable legacy VIRTIO To: Cornelia Huck References: <20201105124353.3680057-1-philmd@redhat.com> <20201105124353.3680057-2-philmd@redhat.com> <20201105140652.6c975b9e.cohuck@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <142c7112-a24f-5349-8969-20c84aee013e@redhat.com> Date: Thu, 5 Nov 2020 14:53:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201105140652.6c975b9e.cohuck@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=63.128.21.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/04 22:46:30 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_H5=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: Elena Ufimtseva , Fam Zheng , Thomas Huth , Jagannathan Raman , qemu-block@nongnu.org, "Michael S. Tsirkin" , Jason Wang , Christian Schoenebeck , Greg Kurz , Wainer dos Santos Moschetta , qemu-devel@nongnu.org, Kevin Wolf , Stefan Hajnoczi , Paolo Bonzini , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Max Reitz , =?UTF-8?Q?Alex_Benn=c3=a9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/5/20 2:06 PM, Cornelia Huck wrote: > On Thu, 5 Nov 2020 13:43:51 +0100 > Philippe Mathieu-Daudé wrote: > >> Per [1] (Terminology): >> >> Legacy interfaces are not required; ie. don’t implement them >> unless you have a need for backwards compatibility! >> >> [2] (Version 1.0): >> >> The device configuration space uses the little-endian format >> for multi-byte fields. >> >> and [3] (Legacy Interface): >> >> for legacy interfaces, device configuration space is generally >> the guest’s native endian, rather than PCI’s little-endian. >> The correct endian-ness is documented for each device. >> >> Add the --disable-virtio-legacy configure flag to produce builds >> with VIRTIO 1.0 only, and the --enable-virtio-legacy to include >> legacy VIRTIO support (supporting legacy VIRTIO is the default). > > This is only dealing with endianess issues; there are other differences > on the control plane as well. > > Currently, virtio-pci has the option to make devices non-transitional, > but virtio-ccw has not (only for device types). For virtio-mmio, you > need to select one of legacy or non-transitional, IIRC. > >> >> [1] http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-60001 >> [2] http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-170003 >> [3] http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-200003 >> >> Signed-off-by: Philippe Mathieu-Daudé >> --- >> configure | 10 ++++++++++ >> meson.build | 1 + >> include/hw/virtio/virtio-access.h | 19 +++++-------------- >> hw/virtio/virtio-legacy.c | 29 +++++++++++++++++++++++++++++ >> hw/virtio/meson.build | 1 + >> 5 files changed, 46 insertions(+), 14 deletions(-) >> create mode 100644 hw/virtio/virtio-legacy.c > > (...) > >> diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h >> index 6818a23a2d3..b6c060f8cc6 100644 >> --- a/include/hw/virtio/virtio-access.h >> +++ b/include/hw/virtio/virtio-access.h >> @@ -20,24 +20,15 @@ >> #include "hw/virtio/virtio.h" >> #include "hw/virtio/virtio-bus.h" >> >> -#if defined(TARGET_PPC64) || defined(TARGET_ARM) >> -#define LEGACY_VIRTIO_IS_BIENDIAN 1 >> -#endif >> - >> +#ifdef CONFIG_VIRTIO_LEGACY >> +bool virtio_access_is_big_endian(VirtIODevice *vdev); >> +#else >> static inline bool virtio_access_is_big_endian(VirtIODevice *vdev) >> { >> -#if defined(LEGACY_VIRTIO_IS_BIENDIAN) >> - return virtio_is_big_endian(vdev); >> -#elif defined(TARGET_WORDS_BIGENDIAN) >> - if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { >> - /* Devices conforming to VIRTIO 1.0 or later are always LE. */ >> - return false; >> - } >> - return true; >> -#else >> + /* Devices conforming to VIRTIO 1.0 or later are always LE. */ >> return false; > > This will make migration from a QEMU that has devices for which 1.0 has > not been negotiated fail. Oh good point... Not as easy as I thought then :/ Now I'm seeing plenty of possible problems. Commits 9b3a35ec823 & d55f518248f help a bit: ("virtio: verify that legacy support is not accidentally on") ("virtio: skip legacy support check on machine types less than 5.1") Thanks for warning :) > >> -#endif >> } >> +#endif >> >> static inline uint16_t virtio_lduw_phys(VirtIODevice *vdev, hwaddr pa) >> { >