need to cope with Arndale's inability to handle Thumb2 KVM guest kernels

[Peter Maydell]

The revision of the A15 on the Arndale boards cannot handle Thumb2 KVM guest kernels (Thumb2 guest userspace is fine). This is unfortunately a hardware issue which cannot be worked around.

 * We need to be doing KVM testing on more than just Arndale (ie TC2 as well) to cover all the use cases
 * We need to have some ARM-kernel test cases so we can do testing on Arndale (worth doing since it's probably going to be a popular board)
 * We should make sure "thumb2 guest kernels on arndale won't work" is documented somewhere useful (in whatever the landing team's equivalent of releasenotes?) to avoid a flood of user confusion

[Tushar Behera (tusharbehera)]

We get a kernel panic while rebooting if THUMB2 support is enabled in kernel. Looking at the bug description, is this an issue with the A15 revision or something wrong with Arndale kernel?

[Fathi Boudra (fboudra)]

On 28 February 2013 07:04, Tushar Behera <email address hidden> wrote:
> We get a kernel panic while rebooting if THUMB2 support is enabled in
> kernel. Looking at the bug description, is this an issue with the A15
> revision or something wrong with Arndale kernel?

The A15 version used on Arndale has a known and documented bug that
prevents the use of MMIO using Thumb2 code.

[Tushar Behera (tusharbehera)]

Given that this is a hardware bug, what is the resolution for this?

[Peter Maydell (pmaydell)]

"We get a kernel panic while rebooting if THUMB2 support is enabled in kernel." -- just to be clear, you mean while booting your host kernel, or your KVM guest kernel?

"what is the resolution for this?" -- my suggestions are described in the initial bug report text.

[Tushar Behera (tusharbehera)]

On 03/07/2013 11:38 AM, Peter Maydell wrote:
> "We get a kernel panic while rebooting if THUMB2 support is enabled in
> kernel." -- just to be clear, you mean while booting your host kernel,
> or your KVM guest kernel?

Yes, the host kernel.

--
Tushar Behera

[Peter Maydell (pmaydell)]

OK, if your host kernel crashes on boot or reboot then that is a different bug. The symptoms of this bug are : host kernel functions perfectly fine, but guest KVM kernel crashes/misbehaves if it is compiled for Thumb2.

Please file a fresh LP bug against the appropriate component for the issues you are seeing.

[Anmar Oueja (anmar)]

I am closing this bug as won't fix since it is a HW issue that we can't do anything about (confirmed with ARM).

Tushar: Please open a separate bug for the host kernel.

[Tushar Behera (tusharbehera)]

On 03/08/2013 04:55 PM, Tushar Behera wrote:
> The issue was because of a hardcoded WFI instruction. Following patch
> fixes the issue.
Just to clarify, this is regarding the host kernel reboot issue with
THUMB2 kernel.

--
Tushar Behera

[Christoffer Dall (cdall)]

Changed to invalid or linaro-kvm: this is not a bug in KVM but a hardware bug we can't do much about.