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[79.183.51.3]) by smtp.gmail.com with ESMTPSA id m15sm7771861wmc.35.2020.04.22.07.25.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Apr 2020 07:25:33 -0700 (PDT) Date: Wed, 22 Apr 2020 10:25:31 -0400 From: "Michael S. Tsirkin" To: Gerd Hoffmann Subject: Re: [PATCH] virtio-vga: fix virtio-vga bar ordering Message-ID: <20200422102504-mutt-send-email-mst@kernel.org> References: <20200421214853.14412-1-anthoine.bourgeois@gmail.com> <20200422020354-mutt-send-email-mst@kernel.org> <20200422104941.qp4lkblm7txlglm2@sirius.home.kraxel.org> MIME-Version: 1.0 In-Reply-To: <20200422104941.qp4lkblm7txlglm2@sirius.home.kraxel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/22 09:07:24 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: Anthoine Bourgeois , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Apr 22, 2020 at 12:49:41PM +0200, Gerd Hoffmann wrote: > On Wed, Apr 22, 2020 at 02:04:36AM -0400, Michael S. Tsirkin wrote: > > On Tue, Apr 21, 2020 at 11:48:53PM +0200, Anthoine Bourgeois wrote: > > > With virtio-vga, pci bar are reordered. Bar #2 is used for compatibil= ity > > > with stdvga. By default, bar #2 is used by virtio modern io bar. > > > This bar is the last one introduce in the virtio pci bar layout and i= t's > > > crushed by the virtio-vga reordering. So virtio-vga and > > > modern-pio-notify are incompatible because virtio-vga failed to > > > initialize with this option. > > >=20 > > > This fix exchange the modern io bar with the modern memory bar, > > > replacing the msix bar that is never impacted anyway. > > >=20 > > > Signed-off-by: Anthoine Bourgeois > >=20 > > Such changes generally need to be tied to machine version. >=20 > Given that modern-pio-notify is off by default and > virtio-vga,modern-pio-notify=3Don is broken I think we don't need to worr= y > about compatibility in this specific case (assuming the patch is updated > to not shuffle around the msix bar, see other reply). >=20 > cheers, > Gerd OK, just worth documenting that this will break cross-version migration if modern-pio-notify is enabled.