From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [RFC/PATCH 1/1] virtio: Introduce MMIO ops Date: Thu, 30 Apr 2020 14:59:50 +0200 Message-ID: <7bf8bffe-267b-6c66-86c9-40017d3ca4c2@siemens.com> References: <1588240976-10213-1-git-send-email-vatsa@codeaurora.org> <1588240976-10213-2-git-send-email-vatsa@codeaurora.org> <20200430101431.GD19932@willie-the-truck> <20200430103446.GH5097@quicinc.com> <20200430104149.GG19932@willie-the-truck> <20200430111156.GI5097@quicinc.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20200430111156.GI5097@quicinc.com> Content-Language: en-US To: Srivatsa Vaddagiri , Will Deacon Cc: konrad.wilk@oracle.com, mst@redhat.com, jasowang@redhat.com, stefano.stabellini@xilinx.com, iommu@lists.linux-foundation.org, virtualization@lists.linux-foundation.org, virtio-dev@lists.oasis-open.org, tsoni@codeaurora.org, pratikp@codeaurora.org, christoffer.dall@arm.com, alex.bennee@linaro.org, linux-kernel@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org On 30.04.20 13:11, Srivatsa Vaddagiri wrote: > * Will Deacon [2020-04-30 11:41:50]: > >> On Thu, Apr 30, 2020 at 04:04:46PM +0530, Srivatsa Vaddagiri wrote: >>> If CONFIG_VIRTIO_MMIO_OPS is defined, then I expect this to be unconditionally >>> set to 'magic_qcom_ops' that uses hypervisor-supported interface for IO (for >>> example: message_queue_send() and message_queue_recevie() hypercalls). >> >> Hmm, but then how would such a kernel work as a guest under all the >> spec-compliant hypervisors out there? > > Ok I see your point and yes for better binary compatibility, the ops have to be > set based on runtime detection of hypervisor capabilities. > >>> Ok. I guess the other option is to standardize on a new virtio transport (like >>> ivshmem2-virtio)? >> >> I haven't looked at that, but I suppose it depends on what your hypervisor >> folks are willing to accomodate. > > I believe ivshmem2_virtio requires hypervisor to support PCI device emulation > (for life-cycle management of VMs), which our hypervisor may not support. A > simple shared memory and doorbell or message-queue based transport will work for > us. As written in our private conversation, a mapping of the ivshmem2 device discovery to platform mechanism (device tree etc.) and maybe even the register access for doorbell and life-cycle management to something hypercall-like would be imaginable. What would count more from virtio perspective is a common mapping on a shared memory transport. That said, I also warned about all the features that PCI already defined (such as message-based interrupts) which you may have to add when going a different way for the shared memory device. Jan -- Siemens AG, Corporate Technology, CT RDA IOT SES-DE Corporate Competence Center Embedded Linux