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Date:   Thu, 2 Jul 2020 15:17:02 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Liu Yi L <yi.l.liu@intel.com>
Cc:     eric.auger@redhat.com, baolu.lu@linux.intel.com, joro@8bytes.org,
        kevin.tian@intel.com, jacob.jun.pan@linux.intel.com,
        ashok.raj@intel.com, jun.j.tian@intel.com, yi.y.sun@intel.com,
        jean-philippe@linaro.org, peterx@redhat.com, hao.wu@intel.com,
        iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 04/14] vfio: Add PASID allocation/free support
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        <1592988927-48009-5-git-send-email-yi.l.liu@intel.com>
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On Wed, 24 Jun 2020 01:55:17 -0700
Liu Yi L <yi.l.liu@intel.com> wrote:

> Shared Virtual Addressing (a.k.a Shared Virtual Memory) allows sharing
> multiple process virtual address spaces with the device for simplified
> programming model. PASID is used to tag an virtual address space in DMA
> requests and to identify the related translation structure in IOMMU. When
> a PASID-capable device is assigned to a VM, we want the same capability
> of using PASID to tag guest process virtual address spaces to achieve
> virtual SVA (vSVA).
> 
> PASID management for guest is vendor specific. Some vendors (e.g. Intel
> VT-d) requires system-wide managed PASIDs cross all devices, regardless
> of whether a device is used by host or assigned to guest. Other vendors
> (e.g. ARM SMMU) may allow PASIDs managed per-device thus could be fully
> delegated to the guest for assigned devices.
> 
> For system-wide managed PASIDs, this patch introduces a vfio module to
> handle explicit PASID alloc/free requests from guest. Allocated PASIDs
> are associated to a process (or, mm_struct) in IOASID core. A vfio_mm
> object is introduced to track mm_struct. Multiple VFIO containers within
> a process share the same vfio_mm object.
> 
> A quota mechanism is provided to prevent malicious user from exhausting
> available PASIDs. Currently the quota is a global parameter applied to
> all VFIO devices. In the future per-device quota might be supported too.
> 
> Cc: Kevin Tian <kevin.tian@intel.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
> v1 -> v2:
> *) added in v2, split from the pasid alloc/free support of v1
> ---
>  drivers/vfio/Kconfig      |   5 ++
>  drivers/vfio/Makefile     |   1 +
>  drivers/vfio/vfio_pasid.c | 151 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/vfio.h      |  28 +++++++++
>  4 files changed, 185 insertions(+)
>  create mode 100644 drivers/vfio/vfio_pasid.c
> 
> diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
> index fd17db9..3d8a108 100644
> --- a/drivers/vfio/Kconfig
> +++ b/drivers/vfio/Kconfig
> @@ -19,6 +19,11 @@ config VFIO_VIRQFD
>  	depends on VFIO && EVENTFD
>  	default n
>  
> +config VFIO_PASID
> +	tristate
> +	depends on IOASID && VFIO
> +	default n
> +
>  menuconfig VFIO
>  	tristate "VFIO Non-Privileged userspace driver framework"
>  	depends on IOMMU_API
> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
> index de67c47..bb836a3 100644
> --- a/drivers/vfio/Makefile
> +++ b/drivers/vfio/Makefile
> @@ -3,6 +3,7 @@ vfio_virqfd-y := virqfd.o
>  
>  obj-$(CONFIG_VFIO) += vfio.o
>  obj-$(CONFIG_VFIO_VIRQFD) += vfio_virqfd.o
> +obj-$(CONFIG_VFIO_PASID) += vfio_pasid.o
>  obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
>  obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
>  obj-$(CONFIG_VFIO_SPAPR_EEH) += vfio_spapr_eeh.o
> diff --git a/drivers/vfio/vfio_pasid.c b/drivers/vfio/vfio_pasid.c
> new file mode 100644
> index 0000000..dd5b6d1
> --- /dev/null
> +++ b/drivers/vfio/vfio_pasid.c
> @@ -0,0 +1,151 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 Intel Corporation.
> + *     Author: Liu Yi L <yi.l.liu@intel.com>
> + *
> + */
> +
> +#include <linux/vfio.h>
> +#include <linux/eventfd.h>
> +#include <linux/file.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/sched/mm.h>
> +
> +#define DRIVER_VERSION  "0.1"
> +#define DRIVER_AUTHOR   "Liu Yi L <yi.l.liu@intel.com>"
> +#define DRIVER_DESC     "PASID management for VFIO bus drivers"
> +
> +#define VFIO_DEFAULT_PASID_QUOTA	1000
> +static int pasid_quota = VFIO_DEFAULT_PASID_QUOTA;
> +module_param_named(pasid_quota, pasid_quota, uint, 0444);
> +MODULE_PARM_DESC(pasid_quota,
> +		 " Set the quota for max number of PASIDs that an application is allowed to request (default 1000)");
> +
> +struct vfio_mm_token {
> +	unsigned long long val;
> +};
> +
> +struct vfio_mm {
> +	struct kref		kref;
> +	struct vfio_mm_token	token;
> +	int			ioasid_sid;
> +	int			pasid_quota;
> +	struct list_head	next;
> +};
> +
> +static struct vfio_pasid {
> +	struct mutex		vfio_mm_lock;
> +	struct list_head	vfio_mm_list;
> +} vfio_pasid;
> +
> +/* called with vfio.vfio_mm_lock held */
> +static void vfio_mm_release(struct kref *kref)
> +{
> +	struct vfio_mm *vmm = container_of(kref, struct vfio_mm, kref);
> +
> +	list_del(&vmm->next);
> +	mutex_unlock(&vfio_pasid.vfio_mm_lock);
> +	ioasid_free_set(vmm->ioasid_sid, true);
> +	kfree(vmm);
> +}
> +
> +void vfio_mm_put(struct vfio_mm *vmm)
> +{
> +	kref_put_mutex(&vmm->kref, vfio_mm_release, &vfio_pasid.vfio_mm_lock);
> +}
> +
> +static void vfio_mm_get(struct vfio_mm *vmm)
> +{
> +	kref_get(&vmm->kref);
> +}
> +
> +struct vfio_mm *vfio_mm_get_from_task(struct task_struct *task)
> +{
> +	struct mm_struct *mm = get_task_mm(task);
> +	struct vfio_mm *vmm;
> +	unsigned long long val = (unsigned long long) mm;
> +	int ret;
> +
> +	mutex_lock(&vfio_pasid.vfio_mm_lock);
> +	/* Search existing vfio_mm with current mm pointer */
> +	list_for_each_entry(vmm, &vfio_pasid.vfio_mm_list, next) {
> +		if (vmm->token.val == val) {
> +			vfio_mm_get(vmm);
> +			goto out;
> +		}
> +	}
> +
> +	vmm = kzalloc(sizeof(*vmm), GFP_KERNEL);
> +	if (!vmm)
> +		return ERR_PTR(-ENOMEM);

lock leaked, mm leaked.

> +
> +	/*
> +	 * IOASID core provides a 'IOASID set' concept to track all
> +	 * PASIDs associated with a token. Here we use mm_struct as
> +	 * the token and create a IOASID set per mm_struct. All the
> +	 * containers of the process share the same IOASID set.
> +	 */
> +	ret = ioasid_alloc_set((struct ioasid_set *) mm, pasid_quota,
> +			       &vmm->ioasid_sid);
> +	if (ret) {
> +		kfree(vmm);
> +		return ERR_PTR(ret);

lock leaked, mm leaked.

> +	}
> +
> +	kref_init(&vmm->kref);
> +	vmm->token.val = (unsigned long long) mm;

We already have it in @val.

> +	vmm->pasid_quota = pasid_quota;

This field on the structure and this assignment seems to serve no
purpose.  Thanks,

Alex

> +
> +	list_add(&vmm->next, &vfio_pasid.vfio_mm_list);
> +out:
> +	mutex_unlock(&vfio_pasid.vfio_mm_lock);
> +	mmput(mm);
> +	return vmm;
> +}
> +
> +int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int max)
> +{
> +	ioasid_t pasid;
> +
> +	pasid = ioasid_alloc(vmm->ioasid_sid, min, max, NULL);
> +
> +	return (pasid == INVALID_IOASID) ? -ENOSPC : pasid;
> +}
> +
> +void vfio_pasid_free_range(struct vfio_mm *vmm,
> +			    ioasid_t min, ioasid_t max)
> +{
> +	ioasid_t pasid = min;
> +
> +	if (min > max)
> +		return;
> +
> +	/*
> +	 * IOASID core will notify PASID users (e.g. IOMMU driver) to
> +	 * teardown necessary structures depending on the to-be-freed
> +	 * PASID.
> +	 */
> +	for (; pasid <= max; pasid++)
> +		ioasid_free(pasid);
> +}
> +
> +static int __init vfio_pasid_init(void)
> +{
> +	mutex_init(&vfio_pasid.vfio_mm_lock);
> +	INIT_LIST_HEAD(&vfio_pasid.vfio_mm_list);
> +	return 0;
> +}
> +
> +static void __exit vfio_pasid_exit(void)
> +{
> +	WARN_ON(!list_empty(&vfio_pasid.vfio_mm_list));
> +}
> +
> +module_init(vfio_pasid_init);
> +module_exit(vfio_pasid_exit);
> +
> +MODULE_VERSION(DRIVER_VERSION);
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR(DRIVER_AUTHOR);
> +MODULE_DESCRIPTION(DRIVER_DESC);
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 38d3c6a..74e077d 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -97,6 +97,34 @@ extern int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops);
>  extern void vfio_unregister_iommu_driver(
>  				const struct vfio_iommu_driver_ops *ops);
>  
> +struct vfio_mm;
> +#if IS_ENABLED(CONFIG_VFIO_PASID)
> +extern struct vfio_mm *vfio_mm_get_from_task(struct task_struct *task);
> +extern void vfio_mm_put(struct vfio_mm *vmm);
> +extern int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int max);
> +extern void vfio_pasid_free_range(struct vfio_mm *vmm,
> +					ioasid_t min, ioasid_t max);
> +#else
> +static inline struct vfio_mm *vfio_mm_get_from_task(struct task_struct *task)
> +{
> +	return NULL;
> +}
> +
> +static inline void vfio_mm_put(struct vfio_mm *vmm)
> +{
> +}
> +
> +static inline int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int max)
> +{
> +	return -ENOTTY;
> +}
> +
> +static inline void vfio_pasid_free_range(struct vfio_mm *vmm,
> +					  ioasid_t min, ioasid_t max)
> +{
> +}
> +#endif /* CONFIG_VFIO_PASID */
> +
>  /*
>   * External user API
>   */