kvm: zapping shadow pages for mmio generation wraparound

kvm: zapping shadow pages for mmio generation wraparound

[Zlatko Calusic]

I'm getting a lot of these in kernel 3.11.0-rc1:

Jul 19 19:53:06 ps kernel: kvm: zapping shadow pages for mmio generation 
wraparound
Jul 19 22:37:47 ps kernel: kvm: zapping shadow pages for mmio generation 
wraparound
Jul 20 00:07:24 ps kernel: kvm: zapping shadow pages for mmio generation 
wraparound
Jul 20 00:11:04 ps kernel: kvm: zapping shadow pages for mmio generation 
wraparound
Jul 20 00:39:14 ps kernel: kvm: zapping shadow pages for mmio generation 
wraparound
Jul 21 00:25:32 ps kernel: kvm: zapping shadow pages for mmio generation 
wraparound

There seems to be one line in the kernel log for every reboot of a WinXP 
guest, and I'm getting a bit bored with it. I don't understand what 
those messages mean? What can I do to stop them flooding the log?

Please Cc: (not subscribed)

Regards,
-- 
Zlatko

Re: kvm: zapping shadow pages for mmio generation wraparound

[Paolo Bonzini]

Il 22/07/2013 22:57, Zlatko Calusic ha scritto:
> I'm getting a lot of these in kernel 3.11.0-rc1:
> 
> Jul 19 19:53:06 ps kernel: kvm: zapping shadow pages for mmio generation
> wraparound
> Jul 19 22:37:47 ps kernel: kvm: zapping shadow pages for mmio generation
> wraparound
> Jul 20 00:07:24 ps kernel: kvm: zapping shadow pages for mmio generation
> wraparound
> Jul 20 00:11:04 ps kernel: kvm: zapping shadow pages for mmio generation
> wraparound
> Jul 20 00:39:14 ps kernel: kvm: zapping shadow pages for mmio generation
> wraparound
> Jul 21 00:25:32 ps kernel: kvm: zapping shadow pages for mmio generation
> wraparound
> 
> There seems to be one line in the kernel log for every reboot of a WinXP
> guest, and I'm getting a bit bored with it. I don't understand what
> those messages mean? What can I do to stop them flooding the log?
> 
> Please Cc: (not subscribed)

The log message would let us correlate any reports with a new
optimization (added in 3.11).  We will probably downgrade it to
KERN_DEBUG before 3.11 goes out (or otherwise cause it to disappear), in
the meanwhile it's harmless.

Paolo

Re: kvm: zapping shadow pages for mmio generation wraparound

[Zlatko Calusic]

On 23.07.2013 13:50, Paolo Bonzini wrote:
> Il 22/07/2013 22:57, Zlatko Calusic ha scritto:
>> I'm getting a lot of these in kernel 3.11.0-rc1:
>>
>> Jul 19 19:53:06 ps kernel: kvm: zapping shadow pages for mmio generation
>> wraparound
>> Jul 19 22:37:47 ps kernel: kvm: zapping shadow pages for mmio generation
>> wraparound
>> Jul 20 00:07:24 ps kernel: kvm: zapping shadow pages for mmio generation
>> wraparound
>> Jul 20 00:11:04 ps kernel: kvm: zapping shadow pages for mmio generation
>> wraparound
>> Jul 20 00:39:14 ps kernel: kvm: zapping shadow pages for mmio generation
>> wraparound
>> Jul 21 00:25:32 ps kernel: kvm: zapping shadow pages for mmio generation
>> wraparound
>>
>> There seems to be one line in the kernel log for every reboot of a WinXP
>> guest, and I'm getting a bit bored with it. I don't understand what
>> those messages mean? What can I do to stop them flooding the log?
>>
>> Please Cc: (not subscribed)
>
> The log message would let us correlate any reports with a new
> optimization (added in 3.11).  We will probably downgrade it to
> KERN_DEBUG before 3.11 goes out (or otherwise cause it to disappear), in
> the meanwhile it's harmless.
>

Ah, OK then. Thanks for the info. And certainly thanks for the great 
virtualization platform!

Best regards,
-- 
Zlatko

Re: kvm: zapping shadow pages for mmio generation wraparound

[Michael Tokarev]

On Tue, 23 Jul 2013 13:50:21 +0200, Paolo Bonzini wrote:
...
> > Jul 21 00:25:32 ps kernel: kvm: zapping shadow pages for mmio generation
> > wraparound
>
> The log message would let us correlate any reports with a new
> optimization (added in 3.11).  We will probably downgrade it to
> KERN_DEBUG before 3.11 goes out (or otherwise cause it to disappear), in
> the meanwhile it's harmless.

Hm.  I just upgraded one of our heavy-kvm-usage host from 3.10 to 3.16,
and it started showing these messages (hence I started searching and
found this thread from 2013).

Has it not been decided to downgrade this message to KERN_DEBUG for some
reason?

What does this message mean anyway?
Why this very rare case (according to comments in arch/x86/kvm/mmu.c)
happens on this machine?

Thanks,

/mjt

Re: kvm: zapping shadow pages for mmio generation wraparound

[Paolo Bonzini]

On 21/12/2014 07:28, Michael Tokarev wrote:
> Has it not been decided to downgrade this message to KERN_DEBUG for some
> reason?

I've just never gotten round to do it.  I'll do it next week.

> What does this message mean anyway?
> Why this very rare case (according to comments in arch/x86/kvm/mmu.c)
> happens on this machine?

It is rare, but we make it happen once per VM to try and avoid that it
bitrots.

Paolo