[MODERATED] Re: [PATCH v5 8/8] NX 8

On 10/10/19 07:53, speck for Pawan Gupta wrote:
> On Wed, Oct 09, 2019 at 05:10:44PM +0200, speck for Paolo Bonzini wrote:
>> On 09/10/19 16:41, speck for Pawan Gupta wrote:
>>> On Wed, Oct 09, 2019 at 08:13:49AM +0200, speck for Paolo Bonzini wrote:
>>>> On 07/10/19 21:45, speck for Pawan Gupta wrote:
>>>>>> Yes, I have other small changes I made so I'll send it out soon together
>>>>>> with a list of preparatory patches that were committed in the past months.
>>>>> Just wanted to add that we would also need to do the backporting and
>>>>> testing soon.
>>>>
>>>> Sure.  With the full list of required patches it shouldn't be an issue.
>>>
>>> When do you think you can post a v6?
>>
>> I have gotten a report of a crash, I'm trying to understand if it's my
>> patches or something pre-existing.  I believe it's the latter, but I'd
>> rather be sure.  I can post v6 right now though.
> 
> We can help debug the crash. Can you please share the series,
> reproduction steps and the crash signature.

The reproduction steps for v5 are as follows:

- grab the next branch of kvm-unit-tests.git[1] and build it

- create a lot of hugepages, on my machine I use 40 GiB worth of them:

  echo 20480 > /proc/sys/vm/nr_hugepages

- load KVM with kvm.nx_huge_pages_recovery_period_secs=3

- run the following script

  while true; do
    echo N > /sys/module/kvm/parameters/nx_huge_pages; sleep 1
    echo Y > /sys/module/kvm/parameters/nx_huge_pages; sleep 5
  done

- run the testcase with

  MEM=40960  # in megabytes
  qemu-kvm -nodefaults -vnc none -serial stdio -kernel x86/hugetext.flat
    -m $MEM -mem-path /dev/hugepages

You can also add a WARN_ON_ONCE(!sp->lpage_disallowed) to
kvm_recover_nx_lpages before the call to kvm_mmu_prepare_zap_page.  As
soon as it triggers, of course everything will go downhill.

Paolo

[1] git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git