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Tsirkin" To: Parav Pandit Cc: Sergio Lopez , "virtio-comment@lists.linux.dev" Subject: Re: [PATCH 1/3] shared-mem: introduce page alignment restrictions Message-ID: <20250304055002-mutt-send-email-mst@kernel.org> References: <20250217115227.4961-1-slp@redhat.com> <20250217115227.4961-2-slp@redhat.com> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: bp2qGSnZEq_pwQXoQ2jsrzFTwGv6NnmvWVcu6Q73_lU_1741085574 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Sun, Feb 23, 2025 at 05:21:00AM +0000, Parav Pandit wrote: > Overall extending pci cap structure is not good idea even though it may appear as small change for below reasons. > > 1. PCI spec already ran out of total bytes that can be stored in the capability section. Extending it will not help. > A virtio level extended capability is not good either due to below guidance from PCI-SIG. > > 2. PCI spec highly discouraged putting vendor specific bits like this in the capability section. > Citation: "It is strongly recommended that PCI Express devices place no registers in Configuration Space other than those in > headers or Capability structures architected by applicable PCI specifications." We can argue about new capabilities, but this is not doing it - it is merely extending the existing one. So I do not really get any of these arguments. I'd be open to an alternative way to discover capabilities, as long as we don't do that, I don't really see a reason to block minor tweaks like this one. At the same time, I am not sure why this is a capability at all. why not in config space? -- MST