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Re: [Qemu-devel] [PATCH v1] kvm/x86: Remove Hyper-V SynIC timer stopping
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From: |
Paolo Bonzini |
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Subject: |
Re: [Qemu-devel] [PATCH v1] kvm/x86: Remove Hyper-V SynIC timer stopping |
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Date: |
Mon, 14 Dec 2015 17:09:24 +0100 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 |
On 14/12/2015 16:33, Andrey Smetanin wrote:
> It's possible that guest send us Hyper-V EOM at the middle
> of Hyper-V SynIC timer running, so we start processing of Hyper-V
> SynIC timers in vcpu context and stop the Hyper-V SynIC timer
> uncoditionally and lose time expiration which Windows 2012R2 guest
> expects.
>
> The patch fixes such situation by not stopping Hyper-V SynIC timer
> at all, because it's safe to restart it without stop in vcpu context
> and timer callback always returns HRTIMER_NORESTART.
Can you summarize with a "picture" what is the bad race?
The patch seems safe, but I'd like to have a better understanding of
what goes wrong.
Paolo