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Thu, 18 Jun 2020 07:56:41 +0000 (UTC) Subject: Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture To: Guilherme Piccoli References: <99779e9c-f05f-501b-b4be-ff719f140a88@canonical.com> <20200616165043.24y2cp53axk7uggy@sirius.home.kraxel.org> <20200616165746.GH2788@work-vm> <084e2640-d71e-d4ec-efdd-3f7947a6b511@redhat.com> From: Laszlo Ersek Message-ID: <1f955c4b-96ea-6751-127a-3590347066e7@redhat.com> Date: Thu, 18 Jun 2020 09:56:40 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=lersek@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/18 01:21:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Pedro Principeza , Eduardo Habkost , Dann Frazier , qemu-devel@nongnu.org, Christian Ehrhardt , "Dr. David Alan Gilbert" , Gerd Hoffmann , fw@gpiccoli.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 06/17/20 18:01, Guilherme Piccoli wrote: > On Wed, Jun 17, 2020 at 12:57 PM Laszlo Ersek wrote: >> [...] >> I don't necessarily see compat issues -- large-BAR PCI device assignment >> might simply stop working under those circumstances, because you could >> no longer use X-PciMmio64Mb, and the new way wouldn't be supported by >> (old) QEMU. >> >> This would indeed be a regression relative to "X-PciMmio64Mb", but >> that's exactly why there's an "X" in "X-PciMmio64Mb". >> > > Are you planning to remove that option, with this improvement? Yes. > I think > we could keep it for a while, as a way to override the automatic > mechanism we might implement. This is even for "safe" purposes, in > case there's some corner case with the auto-sized aperture that we > ignore upfront. I disagree. The knob is called "experimental" specifically so we don't have to introduce even worse complexity for compatibility's sake than what we have now. Graceful deprecation is for options that used to be supported; "X-PciMmio64Mb" has been explicitly experimental from the start. I'm not saying that I'll kill "X-PciMmio64Mb" for sure, just that I very likely will. Thanks Laszlo