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Tsirkin" To: Gerd Hoffmann Cc: qemu-devel@nongnu.org, Paolo Bonzini , Sergio Lopez , Richard Henderson , Marcel Apfelbaum , Eduardo Habkost Subject: Re: [PATCH] microvm: turn off io reservations for pcie root ports Message-ID: <20220629100152-mutt-send-email-mst@kernel.org> References: <20220603085920.604323-1-kraxel@redhat.com> <20220608120505-mutt-send-email-mst@kernel.org> <20220609072838.jcq4cdofpwvlew7j@sirius.home.kraxel.org> <20220627183724-mutt-send-email-mst@kernel.org> <20220629071023.2wfvs7utmx6w3p4o@sirius.home.kraxel.org> <20220629031527-mutt-send-email-mst@kernel.org> <20220629122050.yj7zp2xthtwmigzh@sirius.home.kraxel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220629122050.yj7zp2xthtwmigzh@sirius.home.kraxel.org> Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jun 29, 2022 at 02:20:50PM +0200, Gerd Hoffmann wrote: > On Wed, Jun 29, 2022 at 03:16:17AM -0400, Michael S. Tsirkin wrote: > > On Wed, Jun 29, 2022 at 09:10:23AM +0200, Gerd Hoffmann wrote: > > > On Mon, Jun 27, 2022 at 06:37:50PM -0400, Michael S. Tsirkin wrote: > > > > On Thu, Jun 09, 2022 at 09:28:38AM +0200, Gerd Hoffmann wrote: > > > > > On Wed, Jun 08, 2022 at 12:06:17PM -0400, Michael S. Tsirkin wrote: > > > > > > On Fri, Jun 03, 2022 at 10:59:20AM +0200, Gerd Hoffmann wrote: > > > > > > > The pcie host bridge has no io window on microvm, > > > > > > > so io reservations will not work. > > > > > > > > > > > > > > Signed-off-by: Gerd Hoffmann > > > > > > > > > > > > I don't much like overriding user like this. We end up users > > > > > > setting it to silly values and then if we do want to > > > > > > support this things just break. Thoughts? > > > > > > > > > > Well, it just looked like the simplest way to tell the firmware that > > > > > io reservations are pointless. Do you have a better idea? > > > > > > > > > > take care, > > > > > Gerd > > > > > > > > Fail if user supplies values we can't support. > > > > > > Well, it is the *default* value which doesn't work on microvm. > > > > > > take care, > > > Gerd > > > > Changing defaults is ok of course. Let's just not override the user. > > Ok, so I could use a compat property instead and change the default > for microvm that way. That would allow the user set any value it > wants. And if you like check the value and fail init if not 0. > I still don't see the point though. There is only a single value which > makes sense on microvm. Which is zero. The only effect the user could > archive is make the firmware throwing errors ... > > take care, > Gerd My concern is simple: if right now we override the value then some users might set it to != 0 by mistake. Then if down the road we want to intepret != 0 in some way, these setups will start failing. I don't claim to see a use-case why we'd want to but it's hard to predict the future with certainty. -- MST