From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id C1DD421E49BA1 for ; Tue, 22 Aug 2017 09:59:49 -0700 (PDT) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4373E267C4; Tue, 22 Aug 2017 17:02:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 4373E267C4 Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=lersek@redhat.com Received: from lacos-laptop-7.usersys.redhat.com (ovpn-116-92.phx2.redhat.com [10.3.116.92]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1B62A5D75D; Tue, 22 Aug 2017 17:02:20 +0000 (UTC) To: Ard Biesheuvel , edk2-devel@lists.01.org Cc: leif.lindholm@linaro.org, jordan.l.justen@intel.com References: <20170822163013.12233-1-ard.biesheuvel@linaro.org> From: Laszlo Ersek Message-ID: Date: Tue, 22 Aug 2017 19:02:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170822163013.12233-1-ard.biesheuvel@linaro.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 22 Aug 2017 17:02:22 +0000 (UTC) Subject: Re: [PATCH] ArmVirtPkg: remove QemuVideoDxe from ArmVirtQemu and ArmVirtQemuKernel X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 22 Aug 2017 16:59:50 -0000 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 08/22/17 18:30, Ard Biesheuvel wrote: > One of the reasons for introducing virtio-gpu support to OvmfPkg and > ArmVirtpkg was the fact that under KVM virtualization on ARM, the > legacy VGA cannot be used reliably. This is due to an implementation > detail of QEMU+KVM, which remaps cached host memory into the guest > address space as a framebuffer behind a PCI BAR. Given that the purpose > of a memory mapped framebuffer is its side effects, such BARs should > never be mapped cacheable in the guest, and the mismatched attributes > between host and guest result in a loss of coherency, visible as > corruption in the framebuffer image. > > This issue does not occur under TCG emulation, nor did we expect it to > actually bring down the guest under KVM, and so it was deemed harmless > to keep support for the VGA device as well. However, as it turns out, > the fact that the framebuffer BAR is mapped using device semantics by > default may result in unalignment faults when we use the ordinary string > copy routines on the contents. In theory, we could work around this by > remapping the BAR as write combining, but it appears the generic PCI > bus driver does not actually implement this. > > So let's remove the QemuVideoDxe driver altogether. This may result > in loss of functionality for use cases that rely on the framebuffer > to be directly addressable (such as EFIFB), but given that this never > worked reliably under KVM in the first place, let's not let that stop > us from dropping support for it. > > Contributed-under: TianoCore Contribution Agreement 1.1 > Signed-off-by: Ard Biesheuvel > --- > ArmVirtPkg/ArmVirtQemu.dsc | 2 -- > ArmVirtPkg/ArmVirtQemuFvMain.fdf.inc | 1 - > ArmVirtPkg/ArmVirtQemuKernel.dsc | 2 -- > 3 files changed, 5 deletions(-) > > diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc > index e23a6d17bc44..2e6e76224987 100644 > --- a/ArmVirtPkg/ArmVirtQemu.dsc > +++ b/ArmVirtPkg/ArmVirtQemu.dsc > @@ -57,7 +57,6 @@ > BootLogoLib|MdeModulePkg/Library/BootLogoLib/BootLogoLib.inf > PlatformBootManagerLib|ArmVirtPkg/Library/PlatformBootManagerLib/PlatformBootManagerLib.inf > CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf > - FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf > QemuBootOrderLib|OvmfPkg/Library/QemuBootOrderLib/QemuBootOrderLib.inf > FileExplorerLib|MdeModulePkg/Library/FileExplorerLib/FileExplorerLib.inf > PciPcdProducerLib|ArmVirtPkg/Library/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf > @@ -357,7 +356,6 @@ > # > # Video support > # > - OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf > OvmfPkg/VirtioGpuDxe/VirtioGpu.inf > OvmfPkg/PlatformDxe/Platform.inf > > diff --git a/ArmVirtPkg/ArmVirtQemuFvMain.fdf.inc b/ArmVirtPkg/ArmVirtQemuFvMain.fdf.inc > index 237b2d03a714..3194aa3edc8e 100644 > --- a/ArmVirtPkg/ArmVirtQemuFvMain.fdf.inc > +++ b/ArmVirtPkg/ArmVirtQemuFvMain.fdf.inc > @@ -167,7 +167,6 @@ READ_LOCK_STATUS = TRUE > # > # Video support > # > - INF OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf > INF OvmfPkg/VirtioGpuDxe/VirtioGpu.inf > INF OvmfPkg/PlatformDxe/Platform.inf > > diff --git a/ArmVirtPkg/ArmVirtQemuKernel.dsc b/ArmVirtPkg/ArmVirtQemuKernel.dsc > index aa01debfda69..69de887277cb 100644 > --- a/ArmVirtPkg/ArmVirtQemuKernel.dsc > +++ b/ArmVirtPkg/ArmVirtQemuKernel.dsc > @@ -57,7 +57,6 @@ > BootLogoLib|MdeModulePkg/Library/BootLogoLib/BootLogoLib.inf > PlatformBootManagerLib|ArmVirtPkg/Library/PlatformBootManagerLib/PlatformBootManagerLib.inf > CustomizedDisplayLib|MdeModulePkg/Library/CustomizedDisplayLib/CustomizedDisplayLib.inf > - FrameBufferBltLib|MdeModulePkg/Library/FrameBufferBltLib/FrameBufferBltLib.inf > QemuBootOrderLib|OvmfPkg/Library/QemuBootOrderLib/QemuBootOrderLib.inf > FileExplorerLib|MdeModulePkg/Library/FileExplorerLib/FileExplorerLib.inf > PciPcdProducerLib|ArmVirtPkg/Library/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf > @@ -348,7 +347,6 @@ > # > # Video support > # > - OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf > OvmfPkg/VirtioGpuDxe/VirtioGpu.inf > OvmfPkg/PlatformDxe/Platform.inf > > (My R-b stands; these are comments for a possible followup patch.) Please see: - commit 84a75f70e903 ("OvmfPkg/QemuVideoDxe: enable ARM builds", 2015-02-23), - commit 05a537945872 ("OvmfPkg/QemuVideoDxe: Helper functions for unaligned port I/O.", 2017-04-07)? In my opinion, we should now revert parts of these commits, in one followup patch: - from the first commit, we should revert only the "VALID_ARCHITECTURES" comment change (the rest is built upon by the second commit, and should be preserved) - from the second commit, we should revert the addition of [Sources.ARM, Sources.AARCH64]. This boils down to removing ARM and AARCH64 references from the QemuVideoDxe.inf file. If you agree, could you please submit such a followup patch? Thanks! Laszlo