From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x22f.google.com (mail-wm0-x22f.google.com [IPv6:2a00:1450:400c:c09::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 0B5E421E47D57 for ; Wed, 23 Aug 2017 06:12:47 -0700 (PDT) Received: by mail-wm0-x22f.google.com with SMTP id z132so627803wmg.1 for ; Wed, 23 Aug 2017 06:15:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Z9RcYPvH3NiJVrwciE2ozH7aNb6Ym62C2A210oHnuZg=; b=Vg+i1Q9TSyq00KRPB0k/TdCV3EJ4QIr3m/Lufftl3L9zhkwGJRi4PYEnhMitdicMNW BU/1wiH5+/7aBJdKxt1u7dd04b6VnowGEy0RiTdliKgKuBd77s84rItlRggqcAFEQYXG n3XbvYXS+CaSP28EKyimKeWNrVvTDrDPhS0Vo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=Z9RcYPvH3NiJVrwciE2ozH7aNb6Ym62C2A210oHnuZg=; b=X0CflMLgBGWjfnhdGFiy00FVbuXosbFWHwiY8nd6GdoCV2MHpl9BI4uW3e3R2wv6om oCj1+o8Edj/RMibMfbQfAVBS38SF9cfhTpEpGo6Z5MG3h+Lq5LXTRYfWaEZeFC6j0OZu m/kk9D4sy/MZJ1p59uuBduqpZ53/8M0aS9A+9F7htjFZ1qtZNqDIX6IHxTzb+bg9tZvb lSmovHoQqjX3vEYVTvVXXX1vAKBc0tzZEFyHu8B1TPirKMfNJjm6Wk2YuGBNihYGw7eD gxqC3GyAllSd77gFCnyzgVq2wmcvYsRJiOVvpGTviAT4hmGMYDfAp4/JP/sUPUXz/Vt7 He5g== X-Gm-Message-State: AHYfb5gwwvdk/sVjsVC5PogeeQ3KOrvvdju8s7X0uk6+RzNJK5RfjjBV lPgnTO3OFXjdoxKC X-Received: by 10.28.185.16 with SMTP id j16mr1689706wmf.122.1503494119250; Wed, 23 Aug 2017 06:15:19 -0700 (PDT) Received: from bivouac.eciton.net (bivouac.eciton.net. [2a00:1098:0:86:1000:23:0:2]) by smtp.gmail.com with ESMTPSA id p7sm1217963wrg.9.2017.08.23.06.15.17 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 23 Aug 2017 06:15:18 -0700 (PDT) Date: Wed, 23 Aug 2017 14:15:16 +0100 From: Leif Lindholm To: Ard Biesheuvel Cc: Laszlo Ersek , "edk2-devel@lists.01.org" , Jordan Justen Message-ID: <20170823131516.6f4d2p6jy222ch6m@bivouac.eciton.net> References: <20170822163013.12233-1-ard.biesheuvel@linaro.org> MIME-Version: 1.0 In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) 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: Wed, 23 Aug 2017 13:12:47 -0000 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Aug 22, 2017 at 06:16:56PM +0100, Ard Biesheuvel wrote: > On 22 August 2017 at 18:02, Laszlo Ersek wrote: > > 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? > > Sure, but pending the graphical GRUB discussion. So, after looking at the GRUB code, I am leaning towards agreeing that this is actually not a problem at all ... probably. The efi_gop driver does a Blt() of the entire screen from an off-screen buffer for all updates _unless_ it fails to allocate that off-screen buffer. So, basically, if you run out of memory at that point, it will try to preserve a way to get messages out about that. I will send a question out to grub-devel regarding this behaviour. However, looking at the specification, a question remains over how software can determine whether direct FB access is possible. I mean, a value of 0 seems like a decent hint, but the spec says nothing on the topic. / Leif