From: Paolo Bonzini <pbonzini@redhat.com>
To: 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: Hyper-V tsc page setup
Date: Fri, 22 Jan 2016 12:02:08 +0100 [thread overview]
Message-ID: <56A20C30.4020608@redhat.com> (raw)
In-Reply-To: <56A20131.8090102@virtuozzo.com>
On 22/01/2016 11:15, Andrey Smetanin wrote:
>>
>> - unless KVM can use a master clock, it is incorrect to set up the TSC
>> page this way; the sequence needs to be 0xFFFFFFFF in that case
> 0xFFFFFFFF is not an invalid value for tsc page,
> see https://lkml.org/lkml/2015/11/2/655
oh, I see now.
>> - writing the TSC page must be done while all VCPUs are stopped, because
>> the TSC page doesn't provide the possibility for the guest to retry in
>> the middle of an update (like seqcount in Linux doess)
> I think Windows guest gives tsc page address at boot time and protects
> against other vcpu's tsc page access.
Sometimes the TSC is detected to be unstable and Linux switches to
another clocksource. At least in that case you can get a write to the
TSC page while the guest is running.
In that case it would be enough to write a zero to tsc_sequence, which
_can_ be done atomically while the guest is running. However, KVM
already has a mechanism to stop all VCPUs (KVM_REQ_MASTERCLOCK_UPDATE)
so we might as well use it.
Paolo
next prev parent reply other threads:[~2016-01-22 11:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-24 9:33 [Qemu-devel] [PATCH v1] kvm/x86: Hyper-V tsc page setup Andrey Smetanin
2016-01-05 21:48 ` Peter Hornyack
2016-01-06 9:22 ` Andrey Smetanin
2016-01-12 7:43 ` Andrey Smetanin
2016-01-19 7:48 ` Denis V. Lunev
2016-01-20 14:05 ` Paolo Bonzini
2016-01-20 14:41 ` Andrey Smetanin
2016-01-20 14:44 ` Denis V. Lunev
2016-01-20 14:52 ` Roman Kagan
2016-01-20 14:54 ` Denis V. Lunev
2016-01-20 21:10 ` Paolo Bonzini
2016-01-22 10:08 ` Paolo Bonzini
2016-01-22 10:15 ` Andrey Smetanin
2016-01-22 11:02 ` Paolo Bonzini [this message]
2016-01-22 11:11 ` Andrey Smetanin
2016-01-22 11:31 ` Andrey Smetanin
2016-01-22 11:53 ` Paolo Bonzini
2016-01-22 11:59 ` Andrey Smetanin
2016-01-22 13:13 ` Andrey Smetanin
2016-01-22 13:21 ` Paolo Bonzini
2016-01-22 13:34 ` Andrey Smetanin
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