linux-kernel - Re: [Regression, bisected] a3e06bbe8445f57eb949e6474c5a9b30f24d2057: KVM: emulate lapic tsc deadline timer for guest"

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Date:	Tue, 20 Dec 2011 10:58:37 +0200
From:	Alexey Zaytsev <alexey.zaytsev@...il.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>
Cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	"Garrett D'Amore" <garrett@...enta.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Regression, bisected] a3e06bbe8445f57eb949e6474c5a9b30f24d2057:
 KVM: emulate lapic tsc deadline timer for guest"

On Tue, Dec 20, 2011 at 10:53, Liu, Jinsong <jinsong.liu@...el.com> wrote:
> Alexey Zaytsev wrote:
>> On Wed, Dec 14, 2011 at 11:37, Alexey Zaytsev
>> <alexey.zaytsev@...enta.com> wrote:
>>> On Mon, Dec 12, 2011 at 10:13, Liu, Jinsong <jinsong.liu@...el.com>
>>> wrote:
>>>> Alexey Zaytsev wrote:
>>>>> Hi.
>>>>>
>>>>> After a recent change, qemu --enable-kvm (both 0.15.92 and 1.0)
>>>>> fails to boot illumos. The OS gets stuck pretty late in the boot
>>>>> process, without any hints from the guest. MDB (the illumos
>>>>> kenrnel debugger) failed to clarify the situation at once, the
>>>>> kernel seems to be stuck idling. I've bisected the problem to
>>>>> commit a3e06bbe8445f57eb949e6474c5a9b30f24d2057. Please let me
>>>>> know if you need me to collect any debug information or test any
>>>>> patches.
>>>>
>>>> Alexey,
>>>>
>>>> Does illumos use tsc deadline timer? and do you run it at Intel
>>>> platform?
>>>>
>>>> If yes, would you please help me to collect debug information by
>>>> add some printk points at kvm tsc deadline timer logic? currently I
>>>> totally have no clue to figure out what the issue root from :) and,
>>>> would you please check illumos tsc deadline timer logic by confirm
>>>> whether illumos 1). Enumerate tsc deadline timer capability by
>>>> CPUID; 2). Enable tsc deadline timer mode by lapic MMIO; 3). Start
>>>> tsc deadline timer by WRMSR;
>>>
>>> I think, here's what's going on. We get into
>>> kvm_get_lapic_tscdeadline_msr/kvm_set_lapic_tscdeadline_msr, but qemu
>>> does not use the KVM_CREATE_IRQCHIP ioctl, so we are running without
>>> vcpu->arch.apic and the functions do nothing. And the Linux guest
>>> just handles broken tsc a lot  better, so it survives. Both guests
>>> seem to work fine with qemu-kvm, which uses the ioctl.
>>>
>>
>> Hi. Do you need any more info on thins?
>
> Seems illumos works fine w/ qemu-kvm, that's enough. Maybe you need to wait qemu-kvm sync into qemu?
>

Qemu-kvm is fine for me, but this is a regression and should be fixed.
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