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

From: Jan Kiszka
Subject: Re: [Qemu-devel] vexpress: Framebuffer broken with KVM enabled
Date: Mon, 16 Feb 2015 10:26:07 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

On 2015-02-16 10:20, Anup Patel wrote:
> On Mon, Feb 16, 2015 at 2:43 PM, Jan Kiszka <address@hidden> 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?


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