From: Paolo Bonzini <pbonzini@redhat.com>
To: Andrey Smetanin <asmetanin@virtuozzo.com>, kvm@vger.kernel.org
Cc: Gleb Natapov <gleb@kernel.org>,
Roman Kagan <rkagan@virtuozzo.com>,
"Denis V. Lunev" <den@openvz.org>,
qemu-devel@nongnu.org
Subject: Re: [PATCH v1] kvm/x86: Remove Hyper-V SynIC timer stopping
Date: Mon, 14 Dec 2015 17:09:24 +0100 [thread overview]
Message-ID: <566EE9B4.4040104@redhat.com> (raw)
In-Reply-To: <1450107185-31490-1-git-send-email-asmetanin@virtuozzo.com>
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
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Andrey Smetanin <asmetanin@virtuozzo.com>, kvm@vger.kernel.org
Cc: Gleb Natapov <gleb@kernel.org>, "Denis V. Lunev" <den@openvz.org>,
Roman Kagan <rkagan@virtuozzo.com>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v1] kvm/x86: Remove Hyper-V SynIC timer stopping
Date: Mon, 14 Dec 2015 17:09:24 +0100 [thread overview]
Message-ID: <566EE9B4.4040104@redhat.com> (raw)
In-Reply-To: <1450107185-31490-1-git-send-email-asmetanin@virtuozzo.com>
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
next prev parent reply other threads:[~2015-12-14 16:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-14 15:33 [PATCH v1] kvm/x86: Remove Hyper-V SynIC timer stopping Andrey Smetanin
2015-12-14 15:33 ` [Qemu-devel] " Andrey Smetanin
2015-12-14 16:09 ` Paolo Bonzini [this message]
2015-12-14 16:09 ` Paolo Bonzini
2015-12-14 16:48 ` Andrey Smetanin
2015-12-14 16:48 ` [Qemu-devel] " Andrey Smetanin
2015-12-14 17:01 ` Andrey Smetanin
2015-12-14 17:01 ` [Qemu-devel] " Andrey Smetanin
2015-12-16 17:54 ` Paolo Bonzini
2015-12-16 17:54 ` [Qemu-devel] " Paolo Bonzini
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