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Date:   Thu, 3 Nov 2022 17:11:21 -0700
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Subject: Re: [PATCH v6 13/21] gunyah: vm_mgr: Introduce basic VM Manager
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To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     Bjorn Andersson <quic_bjorande@quicinc.com>,
        Murali Nalajala <quic_mnalajal@quicinc.com>,
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        Sudeep Holla <sudeep.holla@arm.com>,
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From:   Elliot Berman <quic_eberman@quicinc.com>
In-Reply-To: <Y2MKWOihjAPxfl6v@kroah.com>
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On 11/2/2022 5:24 PM, Greg Kroah-Hartman wrote:
> On Wed, Nov 02, 2022 at 11:45:12AM -0700, Elliot Berman wrote:
>> +Michael
>>
>> On 11/1/2022 10:14 PM, Greg Kroah-Hartman wrote:
>>> On Wed, Oct 26, 2022 at 11:58:38AM -0700, Elliot Berman wrote:
>>>> +#define GH_CREATE_VM			_IO(GH_IOCTL_TYPE, 0x40) /* Returns a Gunyah VM fd */
>>>
>>> Why 0x40?  Why not just use the same KVM ioctl numbers and names as you
>>> are doing the same thing as them, right?
>>
>> We've designed so that there are a few ioctls that will feel similar to KVM
>> ioctls since we know this design has been successful, but we don't intend to
>> support KVM ioctls 1:1. Gunyah has different semantics for many of the
>> name-identical ioctls. It seems odd to mix some re-used KVM ioctls with
>> novel Gunyah ioctls?
> 
> Even if you don't support it 1:1, at least for the ones that are the
> same thing, pick the same numbers as that's a nicer thing to do, right?
> 

Does same thing == interpretation of arguments is the same? For
instance, GH_CREATE_VM and KVM_CREATE_VM interpret the arguments
differently. Same for KVM_SET_USERSPACE_MEMORY. The high level 
functionality should be similar for most all hypervisors since they will 
all support creating a VM and probably sharing memory with that VM. The 
arguments for that will necessarily look similar, but they will probably 
be subtly different because the hypervisors support different features.

I don't think userspace that supports both KVM and Gunyah will benefit 
much from re-using the same numbers since those re-used ioctl calls 
still need to sit within the context of a Gunyah VM.

Thanks,
Elliot