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Date: Thu, 4 Mar 2021 13:35:59 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Michael Kelley <mikelley@...rosoft.com>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Cc: "virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"viremana@...ux.microsoft.com" <viremana@...ux.microsoft.com>,
Sunil Muthuswamy <sunilmut@...rosoft.com>,
"wei.liu@...nel.org" <wei.liu@...nel.org>,
Lillian Grassin-Drake <Lillian.GrassinDrake@...rosoft.com>,
KY Srinivasan <kys@...rosoft.com>
Subject: Re: [RFC PATCH 04/18] virt/mshv: request version ioctl
On 2/8/2021 11:41 AM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Friday, November 20, 2020 4:30 PM
>>
>> Reserve ioctl number in userpsace-api/ioctl/ioctl-number.rst
>> Introduce MSHV_REQUEST_VERSION ioctl.
>> Introduce documentation for /dev/mshv in Documentation/virt/mshv
>>
>> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
>> ---
>> .../userspace-api/ioctl/ioctl-number.rst | 2 +
>> Documentation/virt/mshv/api.rst | 62 +++++++++++++++++++
>> include/linux/mshv.h | 11 ++++
>> include/uapi/linux/mshv.h | 19 ++++++
>> virt/mshv/mshv_main.c | 49 +++++++++++++++
>> 5 files changed, 143 insertions(+)
>> create mode 100644 Documentation/virt/mshv/api.rst
>> create mode 100644 include/linux/mshv.h
>> create mode 100644 include/uapi/linux/mshv.h
>>
>> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst
>> b/Documentation/userspace-api/ioctl/ioctl-number.rst
>> index 55a2d9b2ce33..13a4d3ecafca 100644
>> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
>> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
>> @@ -343,6 +343,8 @@ Code Seq# Include File Comments
>> 0xB5 00-0F uapi/linux/rpmsg.h <mailto:linux-
>> remoteproc@...r.kernel.org>
>> 0xB6 all linux/fpga-dfl.h
>> 0xB7 all uapi/linux/remoteproc_cdev.h <mailto:linux-
>> remoteproc@...r.kernel.org>
>> +0xB8 all uapi/linux/mshv.h Microsoft Hypervisor root partition APIs
>> + <mailto:linux-hyperv@...r.kernel.org>
>> 0xC0 00-0F linux/usb/iowarrior.h
>> 0xCA 00-0F uapi/misc/cxl.h
>> 0xCA 10-2F uapi/misc/ocxl.h
>> diff --git a/Documentation/virt/mshv/api.rst b/Documentation/virt/mshv/api.rst
>> new file mode 100644
>> index 000000000000..82e32de48d03
>> --- /dev/null
>> +++ b/Documentation/virt/mshv/api.rst
>> @@ -0,0 +1,62 @@
>> +.. SPDX-License-Identifier: GPL-2.0
>> +
>> +=====================================================
>> +Microsoft Hypervisor Root Partition API Documentation
>> +=====================================================
>> +
>> +1. Overview
>> +===========
>> +
>> +This document describes APIs for creating and managing guest virtual machines
>> +when running Linux as the root partition on the Microsoft Hypervisor.
>> +
>> +This API is not yet stable.
>> +
>> +2. Glossary/Terms
>> +=================
>> +
>> +hv
>> +--
>> +Short for Hyper-V. This name is used in the kernel to describe interfaces to
>> +the Microsoft Hypervisor.
>> +
>> +mshv
>> +----
>> +Short for Microsoft Hypervisor. This is the name of the userland API module
>> +described in this document.
>> +
>> +Partition
>> +---------
>> +A virtual machine running on the Microsoft Hypervisor.
>> +
>> +Root Partition
>> +--------------
>> +The partition that is created and assumes control when the machine boots. The
>> +root partition can use mshv APIs to create guest partitions.
>> +
>> +3. API description
>> +==================
>> +
>> +The module is named mshv and can be configured with CONFIG_HYPERV_ROOT_API.
>> +
>> +Mshv is file descriptor-based, following a similar pattern to KVM.
>> +
>> +To get a handle to the mshv driver, use open("/dev/mshv").
>> +
>> +3.1 MSHV_REQUEST_VERSION
>> +------------------------
>> +:Type: /dev/mshv ioctl
>> +:Parameters: pointer to a u32
>> +:Returns: 0 on success
>> +
>> +Before issuing any other ioctls, a MSHV_REQUEST_VERSION ioctl must be called to
>> +establish the interface version with the kernel module.
>> +
>> +The caller should pass the MSHV_VERSION as an argument.
>> +
>> +The kernel module will check which interface versions it supports and return 0
>> +if one of them matches.
>> +
>> +This /dev/mshv file descriptor will remain 'locked' to that version as long as
>> +it is open - this ioctl can only be called once per open.
>
> To clarify the wording:
>
> The caller should pass the requested version as an argument. If the requested
> version is one that the kernel module supports, the ioctl will return 0. If the
> requested version is not supported by the kernel module, the caller may try
> the ioctl repeatedly to find a version that the caller supports and that the kernel
> module supports. Once a match is found, the /dev/mshv file descriptor is
> 'locked' to that version as long as it is open; i.e., the ioctl can succeed
> only once per open.
>
Thanks, yes that's a bit clearer!
>> +
>> diff --git a/include/linux/mshv.h b/include/linux/mshv.h
>> new file mode 100644
>> index 000000000000..a0982fe2c0b8
>> --- /dev/null
>> +++ b/include/linux/mshv.h
>> @@ -0,0 +1,11 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +#ifndef _LINUX_MSHV_H
>> +#define _LINUX_MSHV_H
>> +
>> +/*
>> + * Microsoft Hypervisor root partition driver for /dev/mshv
>> + */
>> +
>> +#include <uapi/linux/mshv.h>
>> +
>> +#endif
>> diff --git a/include/uapi/linux/mshv.h b/include/uapi/linux/mshv.h
>> new file mode 100644
>> index 000000000000..dd30fc2f0a80
>> --- /dev/null
>> +++ b/include/uapi/linux/mshv.h
>> @@ -0,0 +1,19 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>> +#ifndef _UAPI_LINUX_MSHV_H
>> +#define _UAPI_LINUX_MSHV_H
>> +
>> +/*
>> + * Userspace interface for /dev/mshv
>> + * Microsoft Hypervisor root partition APIs
>> + */
>> +
>> +#include <linux/types.h>
>> +
>> +#define MSHV_VERSION 0x0
>> +
>> +#define MSHV_IOCTL 0xB8
>> +
>> +/* mshv device */
>> +#define MSHV_REQUEST_VERSION _IOW(MSHV_IOCTL, 0x00, __u32)
>> +
>> +#endif
>> diff --git a/virt/mshv/mshv_main.c b/virt/mshv/mshv_main.c
>> index ecb9089761fe..62f631f85301 100644
>> --- a/virt/mshv/mshv_main.c
>> +++ b/virt/mshv/mshv_main.c
>> @@ -11,25 +11,74 @@
>> #include <linux/module.h>
>> #include <linux/fs.h>
>> #include <linux/miscdevice.h>
>> +#include <linux/slab.h>
>> +#include <linux/mshv.h>
>>
>> MODULE_AUTHOR("Microsoft");
>> MODULE_LICENSE("GPL");
>>
>> +#define MSHV_INVALID_VERSION 0xFFFFFFFF
>> +#define MSHV_CURRENT_VERSION MSHV_VERSION
>> +
>> +static u32 supported_versions[] = {
>> + MSHV_CURRENT_VERSION,
>> +};
>
> I'm not sure that the concept of "CURRENT_VERSION" makes sense
> as a fixed constant. We have an array of supported versions, any of
> which are valid and supported by the kernel module. The array
> should list individual versions. The current version is 0, which
> might be labelled as MSHV_VERSION_PRERELEASE, or something
> similar. Then later we might have MSHV_VERSION_RELEASE_1,
> HSMV_VERSION_RELEASE_2, as needed. Or maybe the versions
> are tied to releases of the Microsoft Hypervisor.
>
The idea was that CURRENT_VERSION matches the version in the shared
header file, which would change each release. I can see how this would
be confusing - I will change it as you suggest.
>> +
>> +static long
>> +mshv_ioctl_request_version(u32 *version, void __user *user_arg)
>> +{
>> + u32 arg;
>> + int i;
>> +
>> + if (copy_from_user(&arg, user_arg, sizeof(arg)))
>> + return -EFAULT;
>> +
>> + for (i = 0; i < ARRAY_SIZE(supported_versions); ++i) {
>> + if (supported_versions[i] == arg) {
>> + *version = supported_versions[i];
>> + return 0;
>> + }
>> + }
>> + return -ENOTSUPP;
>> +}
>> +
>> static long
>> mshv_dev_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>> {
>> + u32 *version = (u32 *)filp->private_data;
>> +
>> + if (ioctl == MSHV_REQUEST_VERSION) {
>> + /* Version can only be set once */
>> + if (*version != MSHV_INVALID_VERSION)
>> + return -EBADFD;
>> +
>> + return mshv_ioctl_request_version(version, (void __user *)arg);
>> + }
>> +
>> + /* Version must be set before other ioctls can be called */
>> + if (*version == MSHV_INVALID_VERSION)
>> + return -EBADFD;
>> +
>> + /* TODO other ioctls */
>> +
>> return -ENOTTY;
>> }
>>
>> static int
>> mshv_dev_open(struct inode *inode, struct file *filp)
>> {
>> + filp->private_data = kmalloc(sizeof(u32), GFP_KERNEL);
>> + if (!filp->private_data)
>> + return -ENOMEM;
>> + *(u32 *)filp->private_data = MSHV_INVALID_VERSION;
>> +
>> return 0;
>> }
>>
>> static int
>> mshv_dev_release(struct inode *inode, struct file *filp)
>> {
>> + kfree(filp->private_data);
>> return 0;
>> }
>>
>> --
>> 2.25.1
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