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Re: [Qemu-devel] [PATCH v5 07/16] apic: Open-code timer save/restore

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH v5 07/16] apic: Open-code timer save/restore
Date: Mon, 19 Dec 2011 18:53:16 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110922 Lightning/1.0b2 Thunderbird/3.1.15

On 12/19/2011 06:34 PM, Jan Kiszka wrote:
On 2011-12-20 01:31, Anthony Liguori wrote:
On 12/19/2011 05:45 PM, Jan Kiszka wrote:
On 2011-12-19 23:21, Anthony Liguori wrote:
On 12/15/2011 06:33 AM, Jan Kiszka wrote:
To enable migration between accelerated and non-accelerated APIC
we will need to handle the timer saving and restoring specially and can
no longer rely on the automatics of VMSTATE_TIMER. Specifically,
accelerated model will not start any QEMUTimer.

This patch therefore factors out the generic bits into apic_next_timer
and introduces a post-load callback that can be implemented differently
by both models.

Signed-off-by: Jan Kiszka<address@hidden>

So you basically want the timer to be a dummy field for the in-kernel

Can you fix this up in a pre-save routine (put QEMUTimer into a state
where there isn't an event pending)?

It is not a dummy field, it contains the proper state in both cases. We
just need to convert it to an open-coded state to avoid the QEMUTimer
restoration magic in the in-kernel case (where there must be no

So the state gets fed into the kernel instead of userspace?

Nope. It's kept for eventual use by a user space model.

I think you misunderstood my comments.

When you are using the in-kernel APIC, the is no implementation for the post_load hook. As far as I can tell, the state isn't used.

I know it's used by the user space model but from what I can tell, the value is essentially sync with the in-kernel APIC almost immediately as it happens during KVM_RUN.

So it's a QEMUTimer in the userspace model, but it's just an integer when used in the in-kernel APIC as the timer never fires. It is just saved/restored from and to the kernel.

Is this correct?


Anthony Liguori

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