Re: [PATCH v5 05/15] vfio: Add PASID allocation/free support

Auger Eric
2020-07-20T08:26:26Z

Hi Yi,

On 7/20/20 10:03 AM, Liu, Yi L wrote:
> Hi Eric,
>
>> From: Auger Eric <eric.auger@redhat.com>
>> Sent: Sunday, July 19, 2020 11:39 PM
>>
>> Yi,
>>
>> On 7/12/20 1:21 PM, Liu Yi L 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
>> across?
>
> yep. will correct it.
>
>>> 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>
>>> ---
>>> v4 -> v5:
>>> *) address comments from Eric Auger.
>>> *) address the comments from Alex on the pasid free range support. Added
>>> per vfio_mm pasid r-b tree.
>>> https://lore.kernel.org/kvm/20200709082751.320742ab@x1.home/
>>>
>>> v3 -> v4:
>>> *) fix lock leam in vfio_mm_get_from_task()
>>> *) drop pasid_quota field in struct vfio_mm
>>> *) vfio_mm_get_from_task() returns ERR_PTR(-ENOTTY) when
>>> !CONFIG_VFIO_PASID
>>>
>>> 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 | 235
>> ++++++++++++++++++++++++++++++++++++++++++++++
>>> include/linux/vfio.h | 28 ++++++
>>> 4 files changed, 269 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..66e6054e
>>> --- /dev/null
>>> +++ b/drivers/vfio/vfio_pasid.c
>>> @@ -0,0 +1,235 @@
>>> +// 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)");
>> s/ Set/Set
>
> got it.
>
>>> +
>>> +struct vfio_mm_token {
>>> + unsigned long long val;
>>> +};
>>> +
>>> +struct vfio_mm {
>>> + struct kref kref;
>>> + int ioasid_sid;
>>> + struct mutex pasid_lock;
>>> + struct rb_root pasid_list;
>>> + struct list_head next;
>>> + struct vfio_mm_token token;
>>> +};
>>> +
>>> +static struct mutex vfio_mm_lock;
>>> +static struct list_head vfio_mm_list;
>>> +
>>> +struct vfio_pasid {
>>> + struct rb_node node;
>>> + ioasid_t pasid;
>>> +};
>>> +
>>> +static void vfio_remove_all_pasids(struct vfio_mm *vmm);
>>> +
>>> +/* 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_mm_lock);
>>> + vfio_remove_all_pasids(vmm);
>>> + 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_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_mm_lock);
>>> + /* Search existing vfio_mm with current mm pointer */
>>> + list_for_each_entry(vmm, &vfio_mm_list, next) {
>>> + if (vmm->token.val == val) {
>>> + vfio_mm_get(vmm);
>>> + goto out;
>>> + }
>>> + }
>>> +
>>> + vmm = kzalloc(sizeof(*vmm), GFP_KERNEL);
>>> + if (!vmm) {
>>> + vmm = ERR_PTR(-ENOMEM);
>>> + goto out;
>>> + }
>>> +
>>> + /*
>>> + * 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);
>>> + vmm = ERR_PTR(ret);
>>> + goto out;
>>> + }
>>> +
>>> + kref_init(&vmm->kref);
>>> + vmm->token.val = val;
>>> + mutex_init(&vmm->pasid_lock);
>>> + vmm->pasid_list = RB_ROOT;
>>> +
>>> + list_add(&vmm->next, &vfio_mm_list);
>>> +out:
>>> + mutex_unlock(&vfio_mm_lock);
>>> + mmput(mm);
>>> + return vmm;
>>> +}
>>> +
>>> +/*
>>> + * Find PASID within @min and @max
>>> + */
>>> +static struct vfio_pasid *vfio_find_pasid(struct vfio_mm *vmm,
>>> + ioasid_t min, ioasid_t max)
>>> +{
>>> + struct rb_node *node = vmm->pasid_list.rb_node;
>>> +
>>> + while (node) {
>>> + struct vfio_pasid *vid = rb_entry(node,
>>> + struct vfio_pasid, node);
>>> +
>>> + if (max < vid->pasid)
>>> + node = node->rb_left;
>>> + else if (min > vid->pasid)
>>> + node = node->rb_right;
>>> + else
>>> + return vid;
>>> + }
>>> +
>>> + return NULL;
>>> +}
>>> +
>>> +static void vfio_link_pasid(struct vfio_mm *vmm, struct vfio_pasid
>>> +*new) {
>>> + struct rb_node **link = &vmm->pasid_list.rb_node, *parent = NULL;
>>> + struct vfio_pasid *vid;
>>> +
>>> + while (*link) {
>>> + parent = *link;
>>> + vid = rb_entry(parent, struct vfio_pasid, node);
>>> +
>>> + if (new->pasid <= vid->pasid)
>>> + link = &(*link)->rb_left;
>>> + else
>>> + link = &(*link)->rb_right;
>>> + }
>>> +
>>> + rb_link_node(&new->node, parent, link);
>>> + rb_insert_color(&new->node, &vmm->pasid_list); }
>>> +
>>> +static void vfio_remove_pasid(struct vfio_mm *vmm, struct vfio_pasid
>>> +*vid) {
>>> + rb_erase(&vid->node, &vmm->pasid_list); /* unlink pasid */
>> nit: to be consistent with vfio_unlink_dma, introduce vfio_unlink_pasid
>
> aha, I added it but removed it in the middle of cooking.:-)
>
>>> + ioasid_free(vid->pasid);
>>> + kfree(vid);
>>> +}
>>> +
>>> +static void vfio_remove_all_pasids(struct vfio_mm *vmm) {
>>> + struct rb_node *node;
>>> +
>>> + mutex_lock(&vmm->pasid_lock);
>>> + while ((node = rb_first(&vmm->pasid_list)))
>>> + vfio_remove_pasid(vmm, rb_entry(node, struct vfio_pasid, node));
>>> + mutex_unlock(&vmm->pasid_lock);
>>> +}
>>> +
>>> +int vfio_pasid_alloc(struct vfio_mm *vmm, int min, int max) {
>>> + ioasid_t pasid;
>>> + struct vfio_pasid *vid;
>>> +
>>> + pasid = ioasid_alloc(vmm->ioasid_sid, min, max, NULL);
>>> + if (pasid == INVALID_IOASID)
>>> + return -ENOSPC;
>>> +
>>> + vid = kzalloc(sizeof(*vid), GFP_KERNEL);
>>> + if (!vid) {
>>> + ioasid_free(pasid);
>>> + return -ENOMEM;
>>> + }
>>> +
>>> + vid->pasid = pasid;
>>> +
>>> + mutex_lock(&vmm->pasid_lock);
>>> + vfio_link_pasid(vmm, vid);
>>> + mutex_unlock(&vmm->pasid_lock);
>>> +
>>> + return pasid;
>>> +}
>> I am not totally convinced by your previous reply on EXPORT_SYMBOL_GP()
>> irrelevance in this patch. But well ;-)
>
> I recalled my memory, I think it's made per a comment from Chris.
> I guess it may make sense to export symbols together with the exact
> driver user of it in this patch as well :-) but maybe I misunderstood
> him. if yes, I may add the symbol export back in this patch.
>
> https://lore.kernel.org/linux-iommu/20200331075331.GA26583@infradead.org/#t
OK I don't know the best practice here. Anyway there is no caller at
this stage either. I think you may describe in the commit message the
vfio_iommu_type1 will be the eventual user of the exported functions in
this module, what are the exact exported functions here. You may also
explain the motivation behind creating a separate module.

Thanks

Eric
>
>>
>>> +
>>> +void vfio_pasid_free_range(struct vfio_mm *vmm,
>>> + ioasid_t min, ioasid_t max)
>>> +{
>>> + struct vfio_pasid *vid = NULL;
>>> +
>>> + /*
>>> + * IOASID core will notify PASID users (e.g. IOMMU driver) to
>>> + * teardown necessary structures depending on the to-be-freed
>>> + * PASID.
>>> + */
>>> + mutex_lock(&vmm->pasid_lock);
>>> + while ((vid = vfio_find_pasid(vmm, min, max)) != NULL)
>>> + vfio_remove_pasid(vmm, vid);
>>> + mutex_unlock(&vmm->pasid_lock);
>>> +}
>>> +
>>> +static int __init vfio_pasid_init(void) {
>>> + mutex_init(&vfio_mm_lock);
>>> + INIT_LIST_HEAD(&vfio_mm_list);
>>> + return 0;
>>> +}
>>> +
>>> +static void __exit vfio_pasid_exit(void) {
>>> + WARN_ON(!list_empty(&vfio_mm_list));
>>> +}
>> In your previous reply, ie. https://lkml.org/lkml/2020/7/7/273
>> you said:
>> "
>> I guess yes. VFIO_PASID is supposed to be referenced by VFIO_IOMMU_TYPE1 and
>> may be other module. once vfio_pasid_exit() is triggered, that means its user
>> (VFIO_IOMMU_TYPE1) has been removed. Should all the vfio_mm instances should
>> have been released. If not, means there is vfio_mm leak, should be a bug of user
>> module."
>>
>> if I am not wrong this dependency is not yet known at this stage of
>> the series? I
>> would rather add this comment either in the commit message or here.
>
> make sense, so far it's not known. I can add a comment here. :-)
>
> Regards,
> Yi Liu
>
>> Thanks
>>
>> Eric
>>
>>> +
>>> +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..31472a9 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 ERR_PTR(-ENOTTY);
>>> +}
>>> +
>>> +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
>>> */
>>>