RE: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

Tian, Kevin
2020-03-30T08:32:23Z

> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Sunday, March 22, 2020 8:32 PM
>
> From: Liu Yi L <yi.l.liu@intel.com>
>
> For a long time, devices have only one DMA address space from platform
> IOMMU's point of view. This is true for both bare metal and directed-
> access in virtualization environment. Reason is the source ID of DMA in
> PCIe are BDF (bus/dev/fnc ID), which results in only device granularity

are->is

> DMA isolation. However, this is changing with the latest advancement in
> I/O technology area. More and more platform vendors are utilizing the PCIe
> PASID TLP prefix in DMA requests, thus to give devices with multiple DMA
> address spaces as identified by their individual PASIDs. For example,
> Shared Virtual Addressing (SVA, a.k.a Shared Virtual Memory) is able to
> let device access multiple process virtual address space by binding the

"address space" -> "address spaces"

"binding the" -> "binding each"

> virtual address space with a PASID. Wherein the PASID is allocated in
> software and programmed to device per device specific manner. Devices
> which support PASID capability are called PASID-capable devices. If such
> devices are passed through to VMs, guest software are also able to bind
> guest process virtual address space on such devices. Therefore, the guest
> software could reuse the bare metal software programming model, which
> means guest software will also allocate PASID and program it to device
> directly. This is a dangerous situation since it has potential PASID
> conflicts and unauthorized address space access. It would be safer to
> let host intercept in the guest software's PASID allocation. Thus PASID
> are managed system-wide.
>
> This patch adds VFIO_IOMMU_PASID_REQUEST ioctl which aims to
> passdown
> PASID allocation/free request from the virtual IOMMU. Additionally, such

"Additionally, because such"

> requests are intended to be invoked by QEMU or other applications which

simplify to "intended to be invoked from userspace"

> are running in userspace, it is necessary to have a mechanism to prevent
> single application from abusing available PASIDs in system. With such
> consideration, this patch tracks the VFIO PASID allocation per-VM. There
> was a discussion to make quota to be per assigned devices. e.g. if a VM
> has many assigned devices, then it should have more quota. However, it
> is not sure how many PASIDs an assigned devices will use. e.g. it is

devices -> device

> possible that a VM with multiples assigned devices but requests less
> PASIDs. Therefore per-VM quota would be better.
>
> This patch uses struct mm pointer as a per-VM token. We also considered
> using task structure pointer and vfio_iommu structure pointer. However,
> task structure is per-thread, which means it cannot achieve per-VM PASID
> alloc tracking purpose. While for vfio_iommu structure, it is visible
> only within vfio. Therefore, structure mm pointer is selected. This patch
> adds a structure vfio_mm. A vfio_mm is created when the first vfio
> container is opened by a VM. On the reverse order, vfio_mm is free when
> the last vfio container is released. Each VM is assigned with a PASID
> quota, so that it is not able to request PASID beyond its quota. This
> patch adds a default quota of 1000. This quota could be tuned by
> administrator. Making PASID quota tunable will be added in another patch
> in this series.
>
> Previous discussions:
> https://patchwork.kernel.org/patch/11209429/
>
> Cc: Kevin Tian <kevin.tian@intel.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> drivers/vfio/vfio.c | 130
> ++++++++++++++++++++++++++++++++++++++++
> drivers/vfio/vfio_iommu_type1.c | 104
> ++++++++++++++++++++++++++++++++
> include/linux/vfio.h | 20 +++++++
> include/uapi/linux/vfio.h | 41 +++++++++++++
> 4 files changed, 295 insertions(+)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index c848262..d13b483 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -32,6 +32,7 @@
> #include <linux/vfio.h>
> #include <linux/wait.h>
> #include <linux/sched/signal.h>
> +#include <linux/sched/mm.h>
>
> #define DRIVER_VERSION "0.3"
> #define DRIVER_AUTHOR "Alex Williamson
> <alex.williamson@redhat.com>"
> @@ -46,6 +47,8 @@ static struct vfio {
> struct mutex group_lock;
> struct cdev group_cdev;
> dev_t group_devt;
> + struct list_head vfio_mm_list;
> + struct mutex vfio_mm_lock;
> wait_queue_head_t release_q;
> } vfio;
>
> @@ -2129,6 +2132,131 @@ int vfio_unregister_notifier(struct device *dev,
> enum vfio_notify_type type,
> EXPORT_SYMBOL(vfio_unregister_notifier);
>
> /**
> + * VFIO_MM objects - create, release, get, put, search

why capitalizing vfio_mm?

> + * Caller of the function should have held vfio.vfio_mm_lock.
> + */
> +static struct vfio_mm *vfio_create_mm(struct mm_struct *mm)
> +{
> + struct vfio_mm *vmm;
> + struct vfio_mm_token *token;
> + int ret = 0;
> +
> + vmm = kzalloc(sizeof(*vmm), GFP_KERNEL);
> + if (!vmm)
> + return ERR_PTR(-ENOMEM);
> +
> + /* Per mm IOASID set used for quota control and group operations
> */
> + ret = ioasid_alloc_set((struct ioasid_set *) mm,
> + VFIO_DEFAULT_PASID_QUOTA, &vmm-
> >ioasid_sid);
> + if (ret) {
> + kfree(vmm);
> + return ERR_PTR(ret);
> + }
> +
> + kref_init(&vmm->kref);
> + token = &vmm->token;
> + token->val = mm;
> + vmm->pasid_quota = VFIO_DEFAULT_PASID_QUOTA;
> + mutex_init(&vmm->pasid_lock);
> +
> + list_add(&vmm->vfio_next, &vfio.vfio_mm_list);
> +
> + return vmm;
> +}
> +
> +static void vfio_mm_unlock_and_free(struct vfio_mm *vmm)
> +{
> + /* destroy the ioasid set */
> + ioasid_free_set(vmm->ioasid_sid, true);

do we need hold pasid lock here, since it attempts to destroy a
set which might be referenced by vfio_mm_pasid_free? or is
there guarantee that such race won't happen?

> + mutex_unlock(&vfio.vfio_mm_lock);
> + kfree(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->vfio_next);
> + vfio_mm_unlock_and_free(vmm);
> +}
> +
> +void vfio_mm_put(struct vfio_mm *vmm)
> +{
> + kref_put_mutex(&vmm->kref, vfio_mm_release,
> &vfio.vfio_mm_lock);
> +}
> +EXPORT_SYMBOL_GPL(vfio_mm_put);
> +
> +/* Assume vfio_mm_lock or vfio_mm reference is held */
> +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;
> +
> + mutex_lock(&vfio.vfio_mm_lock);
> + list_for_each_entry(vmm, &vfio.vfio_mm_list, vfio_next) {
> + if (vmm->token.val == val) {
> + vfio_mm_get(vmm);
> + goto out;
> + }
> + }
> +
> + vmm = vfio_create_mm(mm);
> + if (IS_ERR(vmm))
> + vmm = NULL;
> +out:
> + mutex_unlock(&vfio.vfio_mm_lock);
> + mmput(mm);

I assume this has been discussed before, but from readability p.o.v
it might be good to add a comment for this function to explain
how the recording of mm in vfio_mm can be correctly removed
when the mm is being destroyed, since we don't hold a reference
of mm here.

> + return vmm;
> +}
> +EXPORT_SYMBOL_GPL(vfio_mm_get_from_task);
> +
> +int vfio_mm_pasid_alloc(struct vfio_mm *vmm, int min, int max)
> +{
> + ioasid_t pasid;
> + int ret = -ENOSPC;
> +
> + mutex_lock(&vmm->pasid_lock);
> +
> + pasid = ioasid_alloc(vmm->ioasid_sid, min, max, NULL);
> + if (pasid == INVALID_IOASID) {
> + ret = -ENOSPC;
> + goto out_unlock;
> + }
> +
> + ret = pasid;
> +out_unlock:
> + mutex_unlock(&vmm->pasid_lock);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(vfio_mm_pasid_alloc);
> +
> +int vfio_mm_pasid_free(struct vfio_mm *vmm, ioasid_t pasid)
> +{
> + void *pdata;
> + int ret = 0;
> +
> + mutex_lock(&vmm->pasid_lock);
> + pdata = ioasid_find(vmm->ioasid_sid, pasid, NULL);
> + if (IS_ERR(pdata)) {
> + ret = PTR_ERR(pdata);
> + goto out_unlock;
> + }
> + ioasid_free(pasid);
> +
> +out_unlock:
> + mutex_unlock(&vmm->pasid_lock);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(vfio_mm_pasid_free);
> +
> +/**
> * Module/class support
> */
> static char *vfio_devnode(struct device *dev, umode_t *mode)
> @@ -2151,8 +2279,10 @@ static int __init vfio_init(void)
> idr_init(&vfio.group_idr);
> mutex_init(&vfio.group_lock);
> mutex_init(&vfio.iommu_drivers_lock);
> + mutex_init(&vfio.vfio_mm_lock);
> INIT_LIST_HEAD(&vfio.group_list);
> INIT_LIST_HEAD(&vfio.iommu_drivers_list);
> + INIT_LIST_HEAD(&vfio.vfio_mm_list);
> init_waitqueue_head(&vfio.release_q);
>
> ret = misc_register(&vfio_dev);
> diff --git a/drivers/vfio/vfio_iommu_type1.c
> b/drivers/vfio/vfio_iommu_type1.c
> index a177bf2..331ceee 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -70,6 +70,7 @@ struct vfio_iommu {
> unsigned int dma_avail;
> bool v2;
> bool nesting;
> + struct vfio_mm *vmm;
> };
>
> struct vfio_domain {
> @@ -2018,6 +2019,7 @@ static void vfio_iommu_type1_detach_group(void
> *iommu_data,
> static void *vfio_iommu_type1_open(unsigned long arg)
> {
> struct vfio_iommu *iommu;
> + struct vfio_mm *vmm = NULL;
>
> iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
> if (!iommu)
> @@ -2043,6 +2045,10 @@ static void *vfio_iommu_type1_open(unsigned
> long arg)
> iommu->dma_avail = dma_entry_limit;
> mutex_init(&iommu->lock);
> BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
> + vmm = vfio_mm_get_from_task(current);
> + if (!vmm)
> + pr_err("Failed to get vfio_mm track\n");

I assume error should be returned when pr_err is used...

> + iommu->vmm = vmm;
>
> return iommu;
> }
> @@ -2084,6 +2090,8 @@ static void vfio_iommu_type1_release(void
> *iommu_data)
> }
>
> vfio_iommu_iova_free(&iommu->iova_list);
> + if (iommu->vmm)
> + vfio_mm_put(iommu->vmm);
>
> kfree(iommu);
> }
> @@ -2172,6 +2180,55 @@ static int vfio_iommu_iova_build_caps(struct
> vfio_iommu *iommu,
> return ret;
> }
>
> +static bool vfio_iommu_type1_pasid_req_valid(u32 flags)

I don't think you need prefix "vfio_iommu_type1" for every new
function here, especially for leaf internal function as this one.

> +{
> + return !((flags & ~VFIO_PASID_REQUEST_MASK) ||
> + (flags & VFIO_IOMMU_PASID_ALLOC &&
> + flags & VFIO_IOMMU_PASID_FREE));
> +}
> +
> +static int vfio_iommu_type1_pasid_alloc(struct vfio_iommu *iommu,
> + int min,
> + int max)
> +{
> + struct vfio_mm *vmm = iommu->vmm;
> + int ret = 0;
> +
> + mutex_lock(&iommu->lock);
> + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
> + ret = -EFAULT;

why -EFAULT?

> + goto out_unlock;
> + }
> + if (vmm)
> + ret = vfio_mm_pasid_alloc(vmm, min, max);
> + else
> + ret = -EINVAL;
> +out_unlock:
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> +static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> + unsigned int pasid)
> +{
> + struct vfio_mm *vmm = iommu->vmm;
> + int ret = 0;
> +
> + mutex_lock(&iommu->lock);
> + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
> + ret = -EFAULT;

ditto

> + goto out_unlock;
> + }
> +
> + if (vmm)
> + ret = vfio_mm_pasid_free(vmm, pasid);
> + else
> + ret = -EINVAL;
> +out_unlock:
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> static long vfio_iommu_type1_ioctl(void *iommu_data,
> unsigned int cmd, unsigned long arg)
> {
> @@ -2276,6 +2333,53 @@ static long vfio_iommu_type1_ioctl(void
> *iommu_data,
>
> return copy_to_user((void __user *)arg, &unmap, minsz) ?
> -EFAULT : 0;
> +
> + } else if (cmd == VFIO_IOMMU_PASID_REQUEST) {
> + struct vfio_iommu_type1_pasid_request req;
> + unsigned long offset;
> +
> + minsz = offsetofend(struct vfio_iommu_type1_pasid_request,
> + flags);
> +
> + if (copy_from_user(&req, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (req.argsz < minsz ||
> + !vfio_iommu_type1_pasid_req_valid(req.flags))
> + return -EINVAL;
> +
> + if (copy_from_user((void *)&req + minsz,
> + (void __user *)arg + minsz,
> + sizeof(req) - minsz))
> + return -EFAULT;

why copying in two steps instead of copying them together?

> +
> + switch (req.flags & VFIO_PASID_REQUEST_MASK) {
> + case VFIO_IOMMU_PASID_ALLOC:
> + {
> + int ret = 0, result;
> +
> + result = vfio_iommu_type1_pasid_alloc(iommu,
> + req.alloc_pasid.min,
> + req.alloc_pasid.max);
> + if (result > 0) {
> + offset = offsetof(
> + struct
> vfio_iommu_type1_pasid_request,
> + alloc_pasid.result);
> + ret = copy_to_user(
> + (void __user *) (arg + offset),
> + &result, sizeof(result));
> + } else {
> + pr_debug("%s: PASID alloc failed\n",
> __func__);
> + ret = -EFAULT;

no, this branch is not for copy_to_user error. it is about pasid alloc
failure. you should handle both.

> + }
> + return ret;
> + }
> + case VFIO_IOMMU_PASID_FREE:
> + return vfio_iommu_type1_pasid_free(iommu,
> + req.free_pasid);
> + default:
> + return -EINVAL;
> + }
> }
>
> return -ENOTTY;
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index e42a711..75f9f7f1 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -89,6 +89,26 @@ 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);
>
> +#define VFIO_DEFAULT_PASID_QUOTA 1000
> +struct vfio_mm_token {
> + unsigned long long val;
> +};
> +
> +struct vfio_mm {
> + struct kref kref;
> + struct vfio_mm_token token;
> + int ioasid_sid;
> + /* protect @pasid_quota field and pasid allocation/free */
> + struct mutex pasid_lock;
> + int pasid_quota;
> + struct list_head vfio_next;
> +};
> +
> +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_mm_pasid_alloc(struct vfio_mm *vmm, int min, int max);
> +extern int vfio_mm_pasid_free(struct vfio_mm *vmm, ioasid_t pasid);
> +
> /*
> * External user API
> */
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 9e843a1..298ac80 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -794,6 +794,47 @@ struct vfio_iommu_type1_dma_unmap {
> #define VFIO_IOMMU_ENABLE _IO(VFIO_TYPE, VFIO_BASE + 15)
> #define VFIO_IOMMU_DISABLE _IO(VFIO_TYPE, VFIO_BASE + 16)
>
> +/*
> + * PASID (Process Address Space ID) is a PCIe concept which
> + * has been extended to support DMA isolation in fine-grain.
> + * With device assigned to user space (e.g. VMs), PASID alloc
> + * and free need to be system wide. This structure defines
> + * the info for pasid alloc/free between user space and kernel
> + * space.
> + *
> + * @flag=VFIO_IOMMU_PASID_ALLOC, refer to the @alloc_pasid
> + * @flag=VFIO_IOMMU_PASID_FREE, refer to @free_pasid
> + */
> +struct vfio_iommu_type1_pasid_request {
> + __u32 argsz;
> +#define VFIO_IOMMU_PASID_ALLOC (1 << 0)
> +#define VFIO_IOMMU_PASID_FREE (1 << 1)
> + __u32 flags;
> + union {
> + struct {
> + __u32 min;
> + __u32 max;
> + __u32 result;

result->pasid?

> + } alloc_pasid;
> + __u32 free_pasid;

what about putting a common pasid field after flags?

> + };
> +};
> +
> +#define VFIO_PASID_REQUEST_MASK (VFIO_IOMMU_PASID_ALLOC | \
> + VFIO_IOMMU_PASID_FREE)
> +
> +/**
> + * VFIO_IOMMU_PASID_REQUEST - _IOWR(VFIO_TYPE, VFIO_BASE + 22,
> + * struct vfio_iommu_type1_pasid_request)
> + *
> + * Availability of this feature depends on PASID support in the device,
> + * its bus, the underlying IOMMU and the CPU architecture. In VFIO, it
> + * is available after VFIO_SET_IOMMU.
> + *
> + * returns: 0 on success, -errno on failure.
> + */
> +#define VFIO_IOMMU_PASID_REQUEST _IO(VFIO_TYPE, VFIO_BASE +
> 22)
> +
> /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
>
> /*
> --
> 2.7.4