On 08/23/17 15:17, Ard Biesheuvel wrote: > On 23 August 2017 at 14:15, Leif Lindholm <leif.lindh...@linaro.org> wrote: >> On Tue, Aug 22, 2017 at 06:16:56PM +0100, Ard Biesheuvel wrote: >>> On 22 August 2017 at 18:02, Laszlo Ersek <ler...@redhat.com> 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 <ard.biesheu...@linaro.org> >>>>> --- >>>>> 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. >> > > It will assume the FB is accessible unless the pixel format is PixelBltOnly >
Correct, the UEFI spec (v2.7) says in "12.9 Graphics Output Protocol": PixelBltOnly This mode does not support a physical frame buffer. and PixelFormat Enumeration that defines the physical format of the pixel. A value of PixelBltOnly implies that a linear frame buffer is not available for this mode. IIRC simply recognizing and accepting this enum constant was the point of Alex's patch. Thanks Laszlo _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel