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Re: [Qemu-devel] [PATCH v2 3/3] Add rate limiting of RTC_CHANGE, BALLOON

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v2 3/3] Add rate limiting of RTC_CHANGE, BALLOON_CHANGE & WATCHDOG events
Date: Wed, 13 Jun 2012 17:35:47 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0

Il 13/06/2012 17:06, Daniel P. Berrange ha scritto:
> On Wed, Jun 13, 2012 at 04:57:28PM +0200, Paolo Bonzini wrote:
>> Il 13/06/2012 16:53, Daniel P. Berrange ha scritto:
>>>>>>> I don't think SUSPEND can be used to DoS, since once the VM
>>>>>>> is in the suspend state, a monitor command is required to wake
>>>>>>> it up again before the guest OS can trigger a new suspend.
>>>>> Can't the guest OS awake itself?
>>> I didn't think so. Even if it can, we can't rate limit SUSPEND
>>> events in isolation, because they must be strictly ordered
>>> wrt RESUME events.
>> It can program the RTC to awake the OS, but only at 1 wakeup/second.
> Ah that hardware rate limit is good - we don't need todo separate
> throttling with this event then.

Hmm, the ACPI PMTimer could be worse though.  Perhaps we could write a
kvm-unit-test and time how many wakeups we can do per second.


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