Linux Virtualization - Feb 2019 - Regression with "arm64: KVM: Skip MMIO insn after emulation" on 4.4 stable

Hello,

In my testing of crosvm[1] with Linux 4.4.175, I am observing failures
on a 'kevin' Chromebook (RK3399) device - the guest kernel does not
even get to the point of printing its first messages, and the host
seems to be spinning at 100% CPU in KVM_RUN.

I narrowed this down to the 4.4 stable backport of "arm64: KVM: Skip
MMIO insn after emulation" - with this patch reverted, I can boot the
guest kernel as normal again.

Unfortunately, I am unable to easily test with a newer upstream kernel
(this board is using the Chrome OS kernel with many additional patches
applied on top of 4.4), so I'm not sure if this issue was introduced
in the mainline commit or only in the stable branch.  Is it possible
that this patch has other dependencies that were missed in the
backport?  It looks like it was part of a larger series, but only this
patch got pulled for 4.4 stable.

Thanks,
-- Daniel

[1]: https://chromium.googlesource.com/chromiumos/platform/crosvm/

On Wed, Feb 27, 2019 at 04:36:39PM -0800, Daniel Verkamp
wrote:
> Hello,
> 
> In my testing of crosvm[1] with Linux 4.4.175, I am observing failures
> on a 'kevin' Chromebook (RK3399) device - the guest kernel does not
> even get to the point of printing its first messages, and the host
> seems to be spinning at 100% CPU in KVM_RUN.
> 
> I narrowed this down to the 4.4 stable backport of "arm64: KVM: Skip
> MMIO insn after emulation" - with this patch reverted, I can boot the
> guest kernel as normal again.
> 
> Unfortunately, I am unable to easily test with a newer upstream kernel
> (this board is using the Chrome OS kernel with many additional patches
> applied on top of 4.4), so I'm not sure if this issue was introduced
> in the mainline commit or only in the stable branch.  Is it possible
> that this patch has other dependencies that were missed in the
> backport?  It looks like it was part of a larger series, but only this
> patch got pulled for 4.4 stable.
It looks like this got pulled in by Sasha's bot which is why it was
applied.

I have no objection to reverting this if it is causing problems, unless
someone here really thinks it needs to remain in the tree?

thanks,

greg k-h

On Thu, 28 Feb 2019 08:16:05 +0000,
Greg KH <gregkh at linuxfoundation.org> wrote:

Hi both,
> 
> On Wed, Feb 27, 2019 at 04:36:39PM -0800, Daniel Verkamp wrote:
> > Hello,
> > 
> > In my testing of crosvm[1] with Linux 4.4.175, I am observing failures
> > on a 'kevin' Chromebook (RK3399) device - the guest kernel
does not
> > even get to the point of printing its first messages, and the host
> > seems to be spinning at 100% CPU in KVM_RUN.
> > 
> > I narrowed this down to the 4.4 stable backport of "arm64: KVM:
Skip
> > MMIO insn after emulation" - with this patch reverted, I can boot
the
> > guest kernel as normal again.
> > 
> > Unfortunately, I am unable to easily test with a newer upstream kernel
> > (this board is using the Chrome OS kernel with many additional patches
> > applied on top of 4.4), so I'm not sure if this issue was
introduced
> > in the mainline commit or only in the stable branch.  Is it possible
> > that this patch has other dependencies that were missed in the
> > backport?  It looks like it was part of a larger series, but only this
> > patch got pulled for 4.4 stable.
Thanks for reporting this. I'll have a look ASAP.
> It looks like this got pulled in by Sasha's bot which is why it was
> applied.
> 
> I have no objection to reverting this if it is causing problems, unless
> someone here really thinks it needs to remain in the tree?
Can we hold on a tiny bit so that I can verify we haven't regressed
crosvm all the way into mainline?

Daniel, is there any chance you could test with kvmtool as well on
your setup? You can easily compile it as a static binary and run it
from ChromeOS with:

lkvm-static run -c 1 -p "earlycon=uart,mmio,0x3f8" -l Image

which should start a UP guest and drop you to a shell. In the
meantime, I'm starting to build crosvm on my kevin running mainline.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.