Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces

Jonathan Cameron
2018-05-17T14:25:07Z

On Fri, 11 May 2018 20:06:04 +0100
Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org> wrote:

> Allocate IOMMU mm structures and binding them to devices. Four operations
> are added to IOMMU drivers:
>
> * mm_alloc(): to create an io_mm structure and perform architecture-
> specific operations required to grab the process (for instance on ARM,
> pin down the CPU ASID so that the process doesn't get assigned a new
> ASID on rollover).
>
> There is a single valid io_mm structure per Linux mm. Future extensions
> may also use io_mm for kernel-managed address spaces, populated with
> map()/unmap() calls instead of bound to process address spaces. This
> patch focuses on "shared" io_mm.
>
> * mm_attach(): attach an mm to a device. The IOMMU driver checks that the
> device is capable of sharing an address space, and writes the PASID
> table entry to install the pgd.
>
> Some IOMMU drivers will have a single PASID table per domain, for
> convenience. Other can implement it differently but to help these
> drivers, mm_attach and mm_detach take 'attach_domain' and
> 'detach_domain' parameters, that tell whether they need to set and clear
> the PASID entry or only send the required TLB invalidations.
>
> * mm_detach(): detach an mm from a device. The IOMMU driver removes the
> PASID table entry and invalidates the IOTLBs.
>
> * mm_free(): free a structure allocated by mm_alloc(), and let arch
> release the process.
>
> mm_attach and mm_detach operations are serialized with a spinlock. When
> trying to optimize this code, we should at least prevent concurrent
> attach()/detach() on the same domain (so multi-level PASID table code can
> allocate tables lazily). mm_alloc() can sleep, but mm_free must not
> (because we'll have to call it from call_srcu later on).
>
> At the moment we use an IDR for allocating PASIDs and retrieving contexts.
> We also use a single spinlock. These can be refined and optimized later (a
> custom allocator will be needed for top-down PASID allocation).
>
> Keeping track of address spaces requires the use of MMU notifiers.
> Handling process exit with regard to unbind() is tricky, so it is left for
> another patch and we explicitly fail mm_alloc() for the moment.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org>

A few minor bits and bobs inline. Looks good in general + nice diags!

Thanks,

Jonathan

>
> ---
> v1->v2: sanity-check of flags
> ---
> drivers/iommu/iommu-sva.c | 380 +++++++++++++++++++++++++++++++++++++-
> drivers/iommu/iommu.c | 1 +
> include/linux/iommu.h | 28 +++
> 3 files changed, 406 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 8d98f9c09864..6ac679c48f3c 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -5,8 +5,298 @@
> * Copyright (C) 2018 ARM Ltd.
> */
>
> +#include <linux/idr.h>
> #include <linux/iommu.h>
> +#include <linux/sched/mm.h>
> #include <linux/slab.h>
> +#include <linux/spinlock.h>
> +
> +/**
> + * DOC: io_mm model
> + *
> + * The io_mm keeps track of process address spaces shared between CPU and IOMMU.
> + * The following example illustrates the relation between structures
> + * iommu_domain, io_mm and iommu_bond. An iommu_bond is a link between io_mm and
> + * device. A device can have multiple io_mm and an io_mm may be bound to
> + * multiple devices.
> + * ___________________________
> + * | IOMMU domain A |
> + * | ________________ |
> + * | | IOMMU group | +------- io_pgtables
> + * | | | |
> + * | | dev 00:00.0 ----+------- bond --- io_mm X
> + * | |________________| \ |
> + * | '----- bond ---.
> + * |___________________________| \
> + * ___________________________ \
> + * | IOMMU domain B | io_mm Y
> + * | ________________ | / /
> + * | | IOMMU group | | / /
> + * | | | | / /
> + * | | dev 00:01.0 ------------ bond -' /
> + * | | dev 00:01.1 ------------ bond --'
> + * | |________________| |
> + * | +------- io_pgtables
> + * |___________________________|
> + *
> + * In this example, device 00:00.0 is in domain A, devices 00:01.* are in domain
> + * B. All devices within the same domain access the same address spaces. Device
> + * 00:00.0 accesses address spaces X and Y, each corresponding to an mm_struct.
> + * Devices 00:01.* only access address space Y. In addition each
> + * IOMMU_DOMAIN_DMA domain has a private address space, io_pgtable, that is
> + * managed with iommu_map()/iommu_unmap(), and isn't shared with the CPU MMU.
> + *
> + * To obtain the above configuration, users would for instance issue the
> + * following calls:
> + *
> + * iommu_sva_bind_device(dev 00:00.0, mm X, ...) -> PASID 1
> + * iommu_sva_bind_device(dev 00:00.0, mm Y, ...) -> PASID 2
> + * iommu_sva_bind_device(dev 00:01.0, mm Y, ...) -> PASID 2
> + * iommu_sva_bind_device(dev 00:01.1, mm Y, ...) -> PASID 2
> + *
> + * A single Process Address Space ID (PASID) is allocated for each mm. In the
> + * example, devices use PASID 1 to read/write into address space X and PASID 2
> + * to read/write into address space Y.
> + *
> + * Hardware tables describing this configuration in the IOMMU would typically
> + * look like this:
> + *
> + * PASID tables
> + * of domain A
> + * .->+--------+
> + * / 0 | |-------> io_pgtable
> + * / +--------+
> + * Device tables / 1 | |-------> pgd X
> + * +--------+ / +--------+
> + * 00:00.0 | A |-' 2 | |--.
> + * +--------+ +--------+ \
> + * : : 3 | | \
> + * +--------+ +--------+ --> pgd Y
> + * 00:01.0 | B |--. /
> + * +--------+ \ |
> + * 00:01.1 | B |----+ PASID tables |
> + * +--------+ \ of domain B |
> + * '->+--------+ |
> + * 0 | |-- | --> io_pgtable
> + * +--------+ |
> + * 1 | | |
> + * +--------+ |
> + * 2 | |---'
> + * +--------+
> + * 3 | |
> + * +--------+
> + *
> + * With this model, a single call binds all devices in a given domain to an
> + * address space. Other devices in the domain will get the same bond implicitly.
> + * However, users must issue one bind() for each device, because IOMMUs may
> + * implement SVA differently. Furthermore, mandating one bind() per device
> + * allows the driver to perform sanity-checks on device capabilities.
> + *
> + * On Arm and AMD IOMMUs, entry 0 of the PASID table can be used to hold
> + * non-PASID translations. In this case PASID 0 is reserved and entry 0 points
> + * to the io_pgtable base. On Intel IOMMU, the io_pgtable base would be held in
> + * the device table and PASID 0 would be available to the allocator.
> + */
> +
> +struct iommu_bond {
> + struct io_mm *io_mm;
> + struct device *dev;
> + struct iommu_domain *domain;
> +
> + struct list_head mm_head;
> + struct list_head dev_head;
> + struct list_head domain_head;
> +
> + void *drvdata;
> +};
> +
> +/*
> + * Because we're using an IDR, PASIDs are limited to 31 bits (the sign bit is
> + * used for returning errors). In practice implementations will use at most 20
> + * bits, which is the PCI limit.
> + */
> +static DEFINE_IDR(iommu_pasid_idr);
> +
> +/*
> + * For the moment this is an all-purpose lock. It serializes
> + * access/modifications to bonds, access/modifications to the PASID IDR, and
> + * changes to io_mm refcount as well.
> + */
> +static DEFINE_SPINLOCK(iommu_sva_lock);
> +
> +static struct io_mm *
> +io_mm_alloc(struct iommu_domain *domain, struct device *dev,
> + struct mm_struct *mm, unsigned long flags)
> +{
> + int ret;
> + int pasid;
> + struct io_mm *io_mm;
> + struct iommu_sva_param *param = dev->iommu_param->sva_param;
> +
> + if (!domain->ops->mm_alloc || !domain->ops->mm_free)
> + return ERR_PTR(-ENODEV);
> +
> + io_mm = domain->ops->mm_alloc(domain, mm, flags);
> + if (IS_ERR(io_mm))
> + return io_mm;
> + if (!io_mm)
> + return ERR_PTR(-ENOMEM);
> +
> + /*
> + * The mm must not be freed until after the driver frees the io_mm
> + * (which may involve unpinning the CPU ASID for instance, requiring a
> + * valid mm struct.)
> + */
> + mmgrab(mm);
> +
> + io_mm->flags = flags;
> + io_mm->mm = mm;
> + io_mm->release = domain->ops->mm_free;
> + INIT_LIST_HEAD(&io_mm->devices);
> +
> + idr_preload(GFP_KERNEL);
> + spin_lock(&iommu_sva_lock);
> + pasid = idr_alloc(&iommu_pasid_idr, io_mm, param->min_pasid,
> + param->max_pasid + 1, GFP_ATOMIC);

I'd expect the IDR cleanup to be in io_mm_free as that would 'match'
against io_mm_alloc but it's in io_mm_release just before the io_mm_free
call, perhaps move it or am I missing something?

Hmm. This is reworked in patch 5 to use call rcu to do the free. I suppose
we may be burning an idr entry if we take a while to get round to the
free.. If so a comment to explain this would be great.

> + io_mm->pasid = pasid;
> + spin_unlock(&iommu_sva_lock);
> + idr_preload_end();
> +
> + if (pasid < 0) {
> + ret = pasid;
> + goto err_free_mm;
> + }
> +
> + /* TODO: keep track of mm. For the moment, abort. */

>From later patches, I can now see why we didn't init the kref
here, but perhaps a comment would make that clear rather than
people checking it is correctly used throughout? Actually just grab
the comment from patch 5 and put it in this one and that will
do the job nicely.

> + ret = -ENOSYS;
> + spin_lock(&iommu_sva_lock);
> + idr_remove(&iommu_pasid_idr, io_mm->pasid);
> + spin_unlock(&iommu_sva_lock);
> +
> +err_free_mm:
> + domain->ops->mm_free(io_mm);

Really minor, but you now have io_mm->release set so to keep
this obviously the same as the io_mm_free path, perhaps call
that rather than mm_free directly.

> + mmdrop(mm);
> +
> + return ERR_PTR(ret);
> +}
> +
> +static void io_mm_free(struct io_mm *io_mm)
> +{
> + struct mm_struct *mm = io_mm->mm;
> +
> + io_mm->release(io_mm);
> + mmdrop(mm);
> +}
> +
> +static void io_mm_release(struct kref *kref)
> +{
> + struct io_mm *io_mm;
> +
> + io_mm = container_of(kref, struct io_mm, kref);
> + WARN_ON(!list_empty(&io_mm->devices));
> +
> + idr_remove(&iommu_pasid_idr, io_mm->pasid);
> +
> + io_mm_free(io_mm);
> +}
> +
> +/*
> + * Returns non-zero if a reference to the io_mm was successfully taken.
> + * Returns zero if the io_mm is being freed and should not be used.
> + */
> +static int io_mm_get_locked(struct io_mm *io_mm)
> +{
> + if (io_mm)
> + return kref_get_unless_zero(&io_mm->kref);
> +
> + return 0;
> +}
> +
> +static void io_mm_put_locked(struct io_mm *io_mm)
> +{
> + kref_put(&io_mm->kref, io_mm_release);
> +}
> +
> +static void io_mm_put(struct io_mm *io_mm)
> +{
> + spin_lock(&iommu_sva_lock);
> + io_mm_put_locked(io_mm);
> + spin_unlock(&iommu_sva_lock);
> +}
> +
> +static int io_mm_attach(struct iommu_domain *domain, struct device *dev,
> + struct io_mm *io_mm, void *drvdata)
> +{
> + int ret;
> + bool attach_domain = true;
> + int pasid = io_mm->pasid;
> + struct iommu_bond *bond, *tmp;
> + struct iommu_sva_param *param = dev->iommu_param->sva_param;
> +
> + if (!domain->ops->mm_attach || !domain->ops->mm_detach)
> + return -ENODEV;
> +
> + if (pasid > param->max_pasid || pasid < param->min_pasid)
> + return -ERANGE;
> +
> + bond = kzalloc(sizeof(*bond), GFP_KERNEL);
> + if (!bond)
> + return -ENOMEM;
> +
> + bond->domain = domain;
> + bond->io_mm = io_mm;
> + bond->dev = dev;
> + bond->drvdata = drvdata;
> +
> + spin_lock(&iommu_sva_lock);
> + /*
> + * Check if this io_mm is already bound to the domain. In which case the
> + * IOMMU driver doesn't have to install the PASID table entry.
> + */
> + list_for_each_entry(tmp, &domain->mm_list, domain_head) {
> + if (tmp->io_mm == io_mm) {
> + attach_domain = false;
> + break;
> + }
> + }
> +
> + ret = domain->ops->mm_attach(domain, dev, io_mm, attach_domain);
> + if (ret) {
> + kfree(bond);
> + spin_unlock(&iommu_sva_lock);
> + return ret;
> + }
> +
> + list_add(&bond->mm_head, &io_mm->devices);
> + list_add(&bond->domain_head, &domain->mm_list);
> + list_add(&bond->dev_head, &param->mm_list);
> + spin_unlock(&iommu_sva_lock);
> +
> + return 0;
> +}
> +
> +static void io_mm_detach_locked(struct iommu_bond *bond)
> +{
> + struct iommu_bond *tmp;
> + bool detach_domain = true;
> + struct iommu_domain *domain = bond->domain;
> +
> + list_for_each_entry(tmp, &domain->mm_list, domain_head) {
> + if (tmp->io_mm == bond->io_mm && tmp->dev != bond->dev) {
> + detach_domain = false;
> + break;
> + }
> + }
> +
> + domain->ops->mm_detach(domain, bond->dev, bond->io_mm, detach_domain);
> +

I can't see an immediate reason to have a different order in her to the reverse of
the attach above. So I think you should be detaching after the list_del calls.
If there is a reason, can we have a comment so I don't ask on v10.

> + list_del(&bond->mm_head);
> + list_del(&bond->domain_head);
> + list_del(&bond->dev_head);
> + io_mm_put_locked(bond->io_mm);
> +
> + kfree(bond);
> +}
>
> /**
> * iommu_sva_device_init() - Initialize Shared Virtual Addressing for a device
> @@ -47,6 +337,7 @@ int iommu_sva_device_init(struct device *dev, unsigned long features,
>
> param->features = features;
> param->max_pasid = max_pasid;
> + INIT_LIST_HEAD(&param->mm_list);
>
> /*
> * IOMMU driver updates the limits depending on the IOMMU and device
> @@ -114,13 +405,87 @@ EXPORT_SYMBOL_GPL(iommu_sva_device_shutdown);
> int __iommu_sva_bind_device(struct device *dev, struct mm_struct *mm,
> int *pasid, unsigned long flags, void *drvdata)
> {
> - return -ENOSYS; /* TODO */
> + int i, ret = 0;
> + struct io_mm *io_mm = NULL;
> + struct iommu_domain *domain;
> + struct iommu_bond *bond = NULL, *tmp;
> + struct iommu_sva_param *param = dev->iommu_param->sva_param;
> +
> + domain = iommu_get_domain_for_dev(dev);
> + if (!domain)
> + return -EINVAL;
> +
> + /*
> + * The device driver does not call sva_device_init/shutdown and
> + * bind/unbind concurrently, so no need to take the param lock.
> + */
> + if (WARN_ON_ONCE(!param) || (flags & ~param->features))
> + return -EINVAL;
> +
> + /* If an io_mm already exists, use it */
> + spin_lock(&iommu_sva_lock);
> + idr_for_each_entry(&iommu_pasid_idr, io_mm, i) {
> + if (io_mm->mm == mm && io_mm_get_locked(io_mm)) {
> + /* ... Unless it's already bound to this device */
> + list_for_each_entry(tmp, &io_mm->devices, mm_head) {
> + if (tmp->dev == dev) {
> + bond = tmp;

Using bond for this is clear in a sense, but can we not just use ret
so it is obvious here that we are going to return -EEXIST?
At first glance I thought you were going to carry on with this bond
and couldn't work out why it would ever make sense to have two bonds
between a device an an io_mm (which it doesn't!)

> + io_mm_put_locked(io_mm);
> + break;
> + }
> + }
> + break;
> + }
> + }
> + spin_unlock(&iommu_sva_lock);
> +
> + if (bond)
> + return -EEXIST;
> +
> + /* Require identical features within an io_mm for now */
> + if (io_mm && (flags != io_mm->flags)) {
> + io_mm_put(io_mm);
> + return -EDOM;
> + }
> +
> + if (!io_mm) {
> + io_mm = io_mm_alloc(domain, dev, mm, flags);
> + if (IS_ERR(io_mm))
> + return PTR_ERR(io_mm);
> + }
> +
> + ret = io_mm_attach(domain, dev, io_mm, drvdata);
> + if (ret)
> + io_mm_put(io_mm);
> + else
> + *pasid = io_mm->pasid;
> +
> + return ret;
> }
> EXPORT_SYMBOL_GPL(__iommu_sva_bind_device);
>
> int __iommu_sva_unbind_device(struct device *dev, int pasid)
> {
> - return -ENOSYS; /* TODO */
> + int ret = -ESRCH;
> + struct iommu_domain *domain;
> + struct iommu_bond *bond = NULL;
> + struct iommu_sva_param *param = dev->iommu_param->sva_param;
> +
> + domain = iommu_get_domain_for_dev(dev);
> + if (!param || WARN_ON(!domain))
> + return -EINVAL;
> +
> + spin_lock(&iommu_sva_lock);
> + list_for_each_entry(bond, &param->mm_list, dev_head) {
> + if (bond->io_mm->pasid == pasid) {
> + io_mm_detach_locked(bond);
> + ret = 0;
> + break;
> + }
> + }
> + spin_unlock(&iommu_sva_lock);
> +
> + return ret;
> }
> EXPORT_SYMBOL_GPL(__iommu_sva_unbind_device);
>
> @@ -132,6 +497,15 @@ EXPORT_SYMBOL_GPL(__iommu_sva_unbind_device);
> */
> void __iommu_sva_unbind_dev_all(struct device *dev)
> {
> - /* TODO */
> + struct iommu_sva_param *param;
> + struct iommu_bond *bond, *next;
> +
> + param = dev->iommu_param->sva_param;
> + if (param) {
> + spin_lock(&iommu_sva_lock);
> + list_for_each_entry_safe(bond, next, &param->mm_list, dev_head)
> + io_mm_detach_locked(bond);
> + spin_unlock(&iommu_sva_lock);
> + }
> }
> EXPORT_SYMBOL_GPL(__iommu_sva_unbind_dev_all);
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index bd2819deae5b..333801e1519c 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1463,6 +1463,7 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
> domain->type = type;
> /* Assume all sizes by default; the driver may override this later */
> domain->pgsize_bitmap = bus->iommu_ops->pgsize_bitmap;
> + INIT_LIST_HEAD(&domain->mm_list);
>
> return domain;
> }
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index da59c20c4f12..d5f21719a5a0 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -100,6 +100,20 @@ struct iommu_domain {
> void *handler_token;
> struct iommu_domain_geometry geometry;
> void *iova_cookie;
> +
> + struct list_head mm_list;
> +};
> +
> +struct io_mm {
> + int pasid;
> + /* IOMMU_SVA_FEAT_* */
> + unsigned long flags;
> + struct list_head devices;
> + struct kref kref;
> + struct mm_struct *mm;
> +
> + /* Release callback for this mm */
> + void (*release)(struct io_mm *io_mm);
> };
>
> enum iommu_cap {
> @@ -216,6 +230,7 @@ struct iommu_sva_param {
> unsigned long features;
> unsigned int min_pasid;
> unsigned int max_pasid;
> + struct list_head mm_list;
> };
>
> /**
> @@ -227,6 +242,11 @@ struct iommu_sva_param {
> * @detach_dev: detach device from an iommu domain
> * @sva_device_init: initialize Shared Virtual Adressing for a device
> * @sva_device_shutdown: shutdown Shared Virtual Adressing for a device
> + * @mm_alloc: allocate io_mm
> + * @mm_free: free io_mm
> + * @mm_attach: attach io_mm to a device. Install PASID entry if necessary
> + * @mm_detach: detach io_mm from a device. Remove PASID entry and
> + * flush associated TLB entries.
> * @map: map a physically contiguous memory region to an iommu domain
> * @unmap: unmap a physically contiguous memory region from an iommu domain
> * @map_sg: map a scatter-gather list of physically contiguous memory chunks
> @@ -268,6 +288,14 @@ struct iommu_ops {
> struct iommu_sva_param *param);
> void (*sva_device_shutdown)(struct device *dev,
> struct iommu_sva_param *param);
> + struct io_mm *(*mm_alloc)(struct iommu_domain *domain,
> + struct mm_struct *mm,
> + unsigned long flags);
> + void (*mm_free)(struct io_mm *io_mm);
> + int (*mm_attach)(struct iommu_domain *domain, struct device *dev,
> + struct io_mm *io_mm, bool attach_domain);
> + void (*mm_detach)(struct iommu_domain *domain, struct device *dev,
> + struct io_mm *io_mm, bool detach_domain);
> int (*map)(struct iommu_domain *domain, unsigned long iova,
> phys_addr_t paddr, size_t size, int prot);
> size_t (*unmap)(struct iommu_domain *domain, unsigned long iova,