Re: [Qemu-devel] vexpress: Framebuffer broken with KVM enabled

[Jan Kiszka <jan.kiszka@web.de>]

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On 2015-02-16 10:20, Anup Patel wrote:
> On Mon, Feb 16, 2015 at 2:43 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
>> Hi,
>>
>> next issue related to KVM/QEMU on the TK1: The guest image I'm running
>> gives proper framebuffer output when in emulation mode. Once KVM is
>> enabled, the screen is - at best - only initially updated. Sometimes I
>> see the famous tux images and a bit of the console texts, but usually it
>> stays black. Explanations?
> 
> The QEMU accesses Guest Video RAM (or any portion of Guest RAM) as
> cacheable user space memory. The Guest Kernel might access Guest Video
> RAM as non-cacheable to maintain coherency with video device. If this is
> the case then all updates by Guest kernel to Guest Video RAM will not
> be visible to QEMU.

On x86, we manage such RAM as coalesced MMIO region, sync'ing it
periodically or on specific register accesses into the video card model.
I suppose there is nothing like this for the pl111 yet, right?

Jan



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