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Re: [Qemu-devel] cpuid problem in upstream qemu with kvm
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] cpuid problem in upstream qemu with kvm |
Date: |
Tue, 15 Dec 2009 16:28:21 +0200 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Mon, Dec 14, 2009 at 03:49:39PM -0600, Anthony Liguori wrote:
> Michael S. Tsirkin wrote:
>> On Mon, Dec 14, 2009 at 02:54:49PM -0600, Anthony Liguori wrote:
>>
>>> Michael S. Tsirkin wrote:
>>>
>>>> On Mon, Dec 14, 2009 at 02:18:33PM -0600, Anthony Liguori wrote:
>>>>
>>>>> Michael S. Tsirkin wrote:
>>>>>
>>>>>> This might help 32 bit guests, but not guests with 64 bit
>>>>>> kernel and 32 bit userspace (my case) because all 64 bit
>>>>>> CPUs advertise syscall bit in cpuid. Thus 64 bit guests
>>>>>> do not seem to even bother checking this bit:
>>>>>> AMD + 64 bit -> syscall.
>>>>>>
>>>>> Okay, I don't see a great option other than migrating the vendor_id
>>>>> string.
>>>>>
>>>> This won't help with kernels <2.6.32 though. I guess we can switch
>>>> default vendor to Intel, this likely has some other side effects.
>>>>
>>> That's a kernel bug. If we think it effects a lot of users, we
>>> should introduce a CAP such that we can detect this in userspace and
>>> fail gracefully.
>>>
>>
>> Not emulating feature host CPU does not have is a kernel bug?
>> Okay ...
>> Yes, almost no one runs 2.6.32 yet.
>>
>
> The kernel has the ability to filter feature bits from cpuid.
I don't think it does: cpuid is an unpriveledged operation,
is it not?
> We assume
> it's going to filter out things it doesn't support.
It's tricky: this bit has multiple meanings.
This is a cpu architecture bug, not a kernel bug.
> Regards,
>
> Anthony Liguori
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, (continued)
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Michael S. Tsirkin, 2009/12/14
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Anthony Liguori, 2009/12/14
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Michael S. Tsirkin, 2009/12/14
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Anthony Liguori, 2009/12/14
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Michael S. Tsirkin, 2009/12/14
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Anthony Liguori, 2009/12/14
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm,
Michael S. Tsirkin <=
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Anthony Liguori, 2009/12/15
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Michael S. Tsirkin, 2009/12/15
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Avi Kivity, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Avi Kivity, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Anthony Liguori, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Avi Kivity, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Anthony Liguori, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Avi Kivity, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Gleb Natapov, 2009/12/20
- Re: [Qemu-devel] cpuid problem in upstream qemu with kvm, Avi Kivity, 2009/12/20