Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Nuno Das Neves <nunodasneves@linux.microsoft.com>,
        linux-hyperv@vger.kernel.org
Cc:     virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, mikelley@microsoft.com,
        viremana@linux.microsoft.com, sunilmut@microsoft.com,
        nunodasneves@linux.microsoft.com, wei.liu@kernel.org,
        ligrassi@microsoft.com, kys@microsoft.com
Subject: Re: [RFC PATCH 04/18] virt/mshv: request version ioctl
In-Reply-To: <1605918637-12192-5-git-send-email-nunodasneves@linux.microsoft.com>
References: <1605918637-12192-1-git-send-email-nunodasneves@linux.microsoft.com>
 <1605918637-12192-5-git-send-email-nunodasneves@linux.microsoft.com>
Date:   Tue, 09 Feb 2021 14:11:40 +0100
Message-ID: <87y2fxmlmb.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Nuno Das Neves <nunodasneves@linux.microsoft.com> writes:

> 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@linux.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@vger.kernel.org>
>  0xB6  all    linux/fpga-dfl.h
>  0xB7  all    uapi/linux/remoteproc_cdev.h                            <mailto:linux-remoteproc@vger.kernel.org>
> +0xB8  all    uapi/linux/mshv.h                                       Microsoft Hypervisor root partition APIs
> +                                                                     <mailto:linux-hyperv@vger.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.
> +

KVM used to have KVM_GET_API_VERSION too but this turned out to be not
very convenient so we use capabilities (KVM_CHECK_EXTENSION/KVM_ENABLE_CAP)
instead.

> 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,
> +};
> +
> +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;
>  }

-- 
Vitaly