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Wed, 17 Jun 2020 13:25:56 +0000 (UTC) Subject: Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture To: Gerd Hoffmann , Guilherme Piccoli References: <99779e9c-f05f-501b-b4be-ff719f140a88@canonical.com> <20200616165043.24y2cp53axk7uggy@sirius.home.kraxel.org> <20200616165746.GH2788@work-vm> <20200617064014.3j7no7d7trob2ioc@sirius.home.kraxel.org> From: Laszlo Ersek Message-ID: Date: Wed, 17 Jun 2020 15:25:56 +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: <20200617064014.3j7no7d7trob2ioc@sirius.home.kraxel.org> 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=205.139.110.61; envelope-from=lersek@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/17 02:02:46 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_H3=-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 , ehabkost@redhat.com, Dann Frazier , "Dr. David Alan Gilbert" , Christian Ehrhardt , qemu-devel@nongnu.org, fw@gpiccoli.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 06/17/20 08:40, Gerd Hoffmann wrote: > Hi, > >> What if then we have OVMF relying in the physbits *iff* >> "-host-phys-bits" is used > > How can the guest know? Exactly! > Adding "you can trust physbits" bits somewhere (as suggested by Eduardo) > would work for sure, but would depend on a qemu update. > > Maybe a "don't trust physbits in case it is 40" heuristic works well > enough in practice. ... for how many years? ;) No heuristics please. (I absolutely prefer X-PciMmio64Mb to guesswork. With X-PciMmio64Mb, users at least know they have to be careful. I know they don't like that, they just want a promise "it will work forever", but it's not randomly called "experimental", we're not there just yet.) Thank you, Laszlo >> Now, regarding the problem "to trust or not" in the guests' physbits, >> I think it's an orthogonal discussion to some extent. > > It isn't. OVMF can't ignore the problem, you risk to break guests if > you do. > > take care, > Gerd >