[SRU][F][PATCH 0/5] kvm: properly tear down PV features on hibernate

[Andrea Righi]

BugLink: https://bugs.launchpad.net/bugs/1920944

On Thu, May 20, 2021 at 03:36:06PM +0200, Andrea Righi wrote:
> [Impact]
> 
> In LP: #1918694 we applied a fix and a workaround to solve the
> hibernation issues on c5.18xlarge. The workaround was in the form of a
> SAUCE patch:
> 
>   "UBUNTU: SAUCE: aws: kvm: double the size of hv_clock_boot"
> 
> It looks like we can replace this workaround with a proper fix, by
> applying this patch:
> 
> http://next.patchew.org/Linux/20210414123544.1060604-1-vkuznets@redhat.com/
> 
> This is required because various PV features (Async PF, PV EOI, steal
> time) work through memory shared with hypervisor and when we restore
> from hibernation we must properly tear down all these features to make
> sure hypervisor doesn't write to stale locations after we jump to the
> previously hibernated kernel.
> 
> For this reason it is safe to apply this patch set also to the all the
> generic kernels and not just AWS.
> 
> [Test plan]
> 
> This can be easily tested on AWS (but it should be reproduced by
> hibernating any kvm instance with multiple CPUs). Create a c5.18xlarge
> instance, run the memory stress test script (the same test script that
> we are using to stress test hibernation), trigger the hibernate event,
> trigger the resume event. Repeat a couple of times and the problem is
> very likely to happen.
> 
> [Fix]
> 
> On the AWS kernel replace "UBUNTU: SAUCE: aws: kvm: double the size of
> hv_clock_boot" with:
> 
> http://next.patchew.org/Linux/20210414123544.1060604-1-vkuznets@redhat.com/
> 
> For the other kernels, simply apply this patch set.
> 
> The fix has been tested extensively in the AWS infrastructure with
> positive results.
> 
> [Regression potential]
> 
> This new code introduced by the fix can be executed also when a CPU is
> put offline, so we may see potential regressions in the KVM CPU
> hot-plugging.