Re: [PATCH v6 13/21] gunyah: vm_mgr: Introduce basic VM Manager

From: Elliot Berman <quic_eberman@quicinc.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Bjorn Andersson <quic_bjorande@quicinc.com>,
	Murali Nalajala <quic_mnalajal@quicinc.com>,
	Trilok Soni <quic_tsoni@quicinc.com>,
	"Srivatsa Vaddagiri" <quic_svaddagi@quicinc.com>,
	Carl van Schaik <quic_cvanscha@quicinc.com>,
	Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>,
	Andy Gross <agross@kernel.org>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Jassi Brar <jassisinghbrar@gmail.com>,
	<linux-arm-kernel@lists.infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Marc Zyngier <maz@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Jonathan Corbet <corbet@lwn.net>, "Will Deacon" <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
	Amol Maheshwari <amahesh@qti.qualcomm.com>,
	Kalle Valo <kvalo@kernel.org>, <devicetree@vger.kernel.org>,
	<linux-doc@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v6 13/21] gunyah: vm_mgr: Introduce basic VM Manager
Date: Thu, 3 Nov 2022 17:11:21 -0700	[thread overview]
Message-ID: <96238455-73b6-bead-0fdb-55ca68e5bf0b@quicinc.com> (raw)
In-Reply-To: <Y2MKWOihjAPxfl6v@kroah.com>

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

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