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Re: [PATCH 10/18] KVM/MIPS32-VZ: Add API for VZ-ASE Capability

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [PATCH 10/18] KVM/MIPS32-VZ: Add API for VZ-ASE Capability
From: Sanjay Lal <sanjayl@kymasys.com>
Date: Thu, 30 May 2013 11:30:36 -0700
Cc: Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org, linux-mips@linux-mips.org, Ralf Baechle <ralf@linux-mips.org>, Gleb Natapov <gleb@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>
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On May 30, 2013, at 10:07 AM, David Daney wrote:

> On 05/28/2013 09:34 AM, Paolo Bonzini wrote:
>> Il 19/05/2013 07:47, Sanjay Lal ha scritto:
>>> - Add API to allow clients (QEMU etc.) to check whether the H/W
>>>   supports the MIPS VZ-ASE.
>> 
>> Why does this matter to userspace?  Do the userspace have some way to
>> detect if the kernel is unmodified or minimally-modified?
>> 
> 
> There are (will be) two types of VM presented by MIPS KVM:
> 
> 1) That provided by the initial patch where a faux-MIPS is emulated and all 
> kernel code must be in the USEG address space.
> 
> 2) Real MIPS, addressing works as per the architecture specification.
> 
> Presumably the user-space client would like to know which of these are 
> supported, as well as be able to select the desired model.
> 
> I don't know the best way to do this, but I agree that KVM_CAP_MIPS_VZ_ASE is 
> probably not the best name for it.
> 
> My idea was to have the arg of the KVM_CREATE_VM ioctl specify the desired 
> style
> 
> David Daney
> 
> 


Hi Paolo, just wanted to add to David's comments.  KVM/MIPS currently supports 
the two modes David mentioned, based on a kernel config option.   
KVM_CAP_MIPS_VZ_ASE is used by QEMU to make sure that the kvm module currently 
loaded supports the H/W virtualization.

Its a bit cumbersome on MIPS, because you really can't fall back to trap and 
emulate, since the guest kernel for trap and emulate has a user mode link 
address.

I am open to other ways of doing this.

Regards
Sanjay


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