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Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capab
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability |
Date: |
Fri, 10 Jul 2015 17:06:55 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
On 07/10/15 16:59, Paolo Bonzini wrote:
>
>
> On 10/07/2015 16:57, Laszlo Ersek wrote:
>>>> ... In any case, please understand that I'm not campaigning for this
>>>> warning :) IIRC the warning was your (very welcome!) idea after I
>>>> reported the problem; I'm just trying to ensure that the warning match
>>>> the exact issue I encountered.
>>>
>>> Yup. I think the right thing to do would be to hide memory above the
>>> limit.
>> How so?
>>
>> - The stack would not be doing what the user asks for. Pass -m <a_lot>,
>> and the guest would silently see less memory. If the user found out,
>> he'd immediately ask (or set out debugging) why. I think if the user's
>> request cannot be satisfied, the stack should fail hard.
>
> That's another possibility. I think both of them are wrong depending on
> _why_ you're using "-m <a lot>" in the first place.
>
> Considering that this really happens (on Xeons) only for 1TB+ guests,
I reported this issue because I ran into it with a ~64GB guest. From my
/proc/cpuinfo:
model name : Intel(R) Core(TM) i7 CPU M 620 @ 2.67GHz
address sizes : 36 bits physical, 48 bits virtual
I was specifically developing 64GB+ support for OVMF, and this
limitation caused me to think that there was a bug in my OVMF patches.
(There wasn't.) An error message from QEMU, advising me to turn off EPT,
would have saved me many hours.
Thanks
Laszlo
> it's probably just for debugging and then hiding the memory makes some
> sense.
>
> Paolo
>
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, (continued)
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Laszlo Ersek, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Paolo Bonzini, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Bandan Das, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Laszlo Ersek, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Bandan Das, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Laszlo Ersek, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Bandan Das, 2015/07/09
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Paolo Bonzini, 2015/07/10
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Laszlo Ersek, 2015/07/10
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Paolo Bonzini, 2015/07/10
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability,
Laszlo Ersek <=
- Re: [Qemu-devel] [PATCH] KVM: x86: Add host physical address width capability, Bandan Das, 2015/07/10