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Tsirkin" To: Shunsuke Mie Cc: Manivannan Sadhasivam , linux-pci@vger.kernel.org, virtualization@lists.linux.dev, jasowang@redhat.com, xuanzhuo@linux.alibaba.com Subject: Re: [RFC] Legacy Virtio Driver with Device Has Limited Memory Access Message-ID: <20240618061705-mutt-send-email-mst@kernel.org> References: <20240516125913.GC11261@thinkpad> <20240520090809-mutt-send-email-mst@kernel.org> <20240614095033.GA59574@thinkpad> <20240618054115-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Tue, Jun 18, 2024 at 07:15:47PM +0900, Shunsuke Mie wrote: > Thank you for your response. > > 2024年6月18日(火) 18:47 Michael S. Tsirkin : > > > > On Tue, Jun 18, 2024 at 08:41:09AM +0900, Shunsuke Mie wrote: > > > Let's clarify the situation. > > > > > > The Virtio device and driver are not working properly due to a > > > combination of the following reasons: > > > > > > 1. Regarding VIRTIO_F_ACCESS_PLATFORM: > > > - The modern spec includes VIRTIO_F_ACCESS_PLATFORM, which allows > > > Physical DMAC to be used. > > > - This feature is not available in the legacy spec. > > > > ... because legacy drivers don't set it > > > > > 2. Regarding Virtio PCIe Capability: > > > - The modern spec requires Virtio PCIe Capability. > > > > It's a PCI capability actually. People have been asking > > about option to make it a pcie extended capability, > > but no one did the spec, qemu and driver work, yet. > > > > > - In some environments, Virtio PCIe Capability cannot be provided. > > > > why not? > PCIe Endpoint Controller chips are available from several vendors and allow > software to describe the behavior of PCIe Endpoint functions. However, they > offer only limited functionality. Specifically, while PCIe bus communication is > programmable, PCIe Capabilities are fixed and cannot be made to show as > virtio's. Okay. So where could these structures live, if not in pci config? -- MST