Re: [PATCH kernel v9 31/32] vfio: powerpc/spapr: Support multiple groups in one container if possible

David Gibson
2015-04-30T07:45:26Z

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On Sat, Apr 25, 2015 at 10:14:55PM +1000, Alexey Kardashevskiy wrote:
> At the moment only one group per container is supported.
> POWER8 CPUs have more flexible design and allows naving 2 TCE tables per
> IOMMU group so we can relax this limitation and support multiple groups
> per container.

It's not obvious why allowing multiple TCE tables per PE has any
pearing on allowing multiple groups per container.

> This adds TCE table descriptors to a container and uses iommu_table_group_ops
> to create/set DMA windows on IOMMU groups so the same TCE tables will be
> shared between several IOMMU groups.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> [aw: for the vfio related changes]
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> Changes:
> v7:
> * updated doc
> ---
> Documentation/vfio.txt | 8 +-
> drivers/vfio/vfio_iommu_spapr_tce.c | 268 ++++++++++++++++++++++++++----------
> 2 files changed, 199 insertions(+), 77 deletions(-)
>
> diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt
> index 94328c8..7dcf2b5 100644
> --- a/Documentation/vfio.txt
> +++ b/Documentation/vfio.txt
> @@ -289,10 +289,12 @@ PPC64 sPAPR implementation note
>
> This implementation has some specifics:
>
> -1) Only one IOMMU group per container is supported as an IOMMU group
> -represents the minimal entity which isolation can be guaranteed for and
> -groups are allocated statically, one per a Partitionable Endpoint (PE)
> +1) On older systems (POWER7 with P5IOC2/IODA1) only one IOMMU group per
> +container is supported as an IOMMU table is allocated at the boot time,
> +one table per a IOMMU group which is a Partitionable Endpoint (PE)
> (PE is often a PCI domain but not always).

I thought the more fundamental problem was that different PEs tended
to use disjoint bus address ranges, so even by duplicating put_tce
across PEs you couldn't have a common address space.

> +Newer systems (POWER8 with IODA2) have improved hardware design which allows
> +to remove this limitation and have multiple IOMMU groups per a VFIO container.
>
> 2) The hardware supports so called DMA windows - the PCI address range
> within which DMA transfer is allowed, any attempt to access address space
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index a7d6729..970e3a2 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -82,6 +82,11 @@ static void decrement_locked_vm(long npages)
> * into DMA'ble space using the IOMMU
> */
>
> +struct tce_iommu_group {
> + struct list_head next;
> + struct iommu_group *grp;
> +};
> +
> /*
> * The container descriptor supports only a single group per container.
> * Required by the API as the container is not supplied with the IOMMU group
> @@ -89,10 +94,11 @@ static void decrement_locked_vm(long npages)
> */
> struct tce_container {
> struct mutex lock;
> - struct iommu_group *grp;
> bool enabled;
> unsigned long locked_pages;
> bool v2;
> + struct iommu_table tables[IOMMU_TABLE_GROUP_MAX_TABLES];

Hrm, so here we have more copies of the full iommu_table structures,
which again muddies the lifetime. The table_group pointer is
presumably meaningless in these copies, which seems dangerously
confusing.

> + struct list_head group_list;
> };
>
> static long tce_unregister_pages(struct tce_container *container,
> @@ -154,20 +160,20 @@ static bool tce_page_is_contained(struct page *page, unsigned page_shift)
> return (PAGE_SHIFT + compound_order(compound_head(page))) >= page_shift;
> }
>
> +static inline bool tce_groups_attached(struct tce_container *container)
> +{
> + return !list_empty(&container->group_list);
> +}
> +
> static struct iommu_table *spapr_tce_find_table(
> struct tce_container *container,
> phys_addr_t ioba)
> {
> long i;
> struct iommu_table *ret = NULL;
> - struct iommu_table_group *table_group;
> -
> - table_group = iommu_group_get_iommudata(container->grp);
> - if (!table_group)
> - return NULL;
>
> for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> - struct iommu_table *tbl = &table_group->tables[i];
> + struct iommu_table *tbl = &container->tables[i];
> unsigned long entry = ioba >> tbl->it_page_shift;
> unsigned long start = tbl->it_offset;
> unsigned long end = start + tbl->it_size;
> @@ -186,9 +192,7 @@ static int tce_iommu_enable(struct tce_container *container)
> int ret = 0;
> unsigned long locked;
> struct iommu_table_group *table_group;
> -
> - if (!container->grp)
> - return -ENXIO;
> + struct tce_iommu_group *tcegrp;
>
> if (!current->mm)
> return -ESRCH; /* process exited */
> @@ -225,7 +229,12 @@ static int tce_iommu_enable(struct tce_container *container)
> * as there is no way to know how much we should increment
> * the locked_vm counter.
> */
> - table_group = iommu_group_get_iommudata(container->grp);
> + if (!tce_groups_attached(container))
> + return -ENODEV;
> +
> + tcegrp = list_first_entry(&container->group_list,
> + struct tce_iommu_group, next);
> + table_group = iommu_group_get_iommudata(tcegrp->grp);
> if (!table_group)
> return -ENODEV;
>
> @@ -257,6 +266,48 @@ static void tce_iommu_disable(struct tce_container *container)
> decrement_locked_vm(container->locked_pages);
> }
>
> +static long tce_iommu_create_table(struct iommu_table_group *table_group,
> + int num,
> + __u32 page_shift,
> + __u64 window_size,
> + __u32 levels,
> + struct iommu_table *tbl)

With multiple groups (and therefore PEs) per container, this seems
wrong. There's only one table_group per PE, so what's special about
PE whose table group is passed in here.

> +{
> + long ret, table_size;
> +
> + table_size = table_group->ops->get_table_size(page_shift, window_size,
> + levels);
> + if (!table_size)
> + return -EINVAL;
> +
> + ret = try_increment_locked_vm(table_size >> PAGE_SHIFT);
> + if (ret)
> + return ret;
> +
> + ret = table_group->ops->create_table(table_group, num,
> + page_shift, window_size, levels, tbl);
> +
> + WARN_ON(!ret && !tbl->it_ops->free);
> + WARN_ON(!ret && (tbl->it_allocated_size != table_size));
> +
> + if (ret)
> + decrement_locked_vm(table_size >> PAGE_SHIFT);
> +
> + return ret;
> +}
> +
> +static void tce_iommu_free_table(struct iommu_table *tbl)
> +{
> + unsigned long pages = tbl->it_allocated_size >> PAGE_SHIFT;
> +
> + if (!tbl->it_size)
> + return;
> +
> + tbl->it_ops->free(tbl);

So, this is exactly the case where the lifetimes are badly confusing.
How can you be confident here that another copy of the iommu_table
struct isn't referencing the same TCE tables?

> + decrement_locked_vm(pages);
> + memset(tbl, 0, sizeof(*tbl));
> +}
> +
> static void *tce_iommu_open(unsigned long arg)
> {
> struct tce_container *container;
> @@ -271,19 +322,41 @@ static void *tce_iommu_open(unsigned long arg)
> return ERR_PTR(-ENOMEM);
>
> mutex_init(&container->lock);
> + INIT_LIST_HEAD_RCU(&container->group_list);

I see no other mentions of rcu related to this list, which doesn't
seem right.

> container->v2 = arg == VFIO_SPAPR_TCE_v2_IOMMU;
>
> return container;
> }
>
> +static int tce_iommu_clear(struct tce_container *container,
> + struct iommu_table *tbl,
> + unsigned long entry, unsigned long pages);
> +
> static void tce_iommu_release(void *iommu_data)
> {
> struct tce_container *container = iommu_data;
> + struct iommu_table_group *table_group;
> + struct tce_iommu_group *tcegrp;
> + long i;
>
> - WARN_ON(container->grp);
> + while (tce_groups_attached(container)) {
> + tcegrp = list_first_entry(&container->group_list,
> + struct tce_iommu_group, next);
> + table_group = iommu_group_get_iommudata(tcegrp->grp);
> + tce_iommu_detach_group(iommu_data, tcegrp->grp);
> + }
>
> - if (container->grp)
> - tce_iommu_detach_group(iommu_data, container->grp);
> + /*
> + * If VFIO created a table, it was not disposed
> + * by tce_iommu_detach_group() so do it now.
> + */
> + for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> + struct iommu_table *tbl = &container->tables[i];
> +
> + tce_iommu_clear(container, tbl, tbl->it_offset, tbl->it_size);
> + tce_iommu_free_table(tbl);
> + }
>
> tce_iommu_disable(container);
> mutex_destroy(&container->lock);
> @@ -509,12 +582,15 @@ static long tce_iommu_ioctl(void *iommu_data,
>
> case VFIO_IOMMU_SPAPR_TCE_GET_INFO: {
> struct vfio_iommu_spapr_tce_info info;
> + struct tce_iommu_group *tcegrp;
> struct iommu_table_group *table_group;
>
> - if (WARN_ON(!container->grp))
> + if (!tce_groups_attached(container))
> return -ENXIO;
>
> - table_group = iommu_group_get_iommudata(container->grp);
> + tcegrp = list_first_entry(&container->group_list,
> + struct tce_iommu_group, next);
> + table_group = iommu_group_get_iommudata(tcegrp->grp);
>
> if (!table_group)
> return -ENXIO;
> @@ -707,12 +783,20 @@ static long tce_iommu_ioctl(void *iommu_data,
> tce_iommu_disable(container);
> mutex_unlock(&container->lock);
> return 0;
> - case VFIO_EEH_PE_OP:
> - if (!container->grp)
> - return -ENODEV;
>
> - return vfio_spapr_iommu_eeh_ioctl(container->grp,
> - cmd, arg);
> + case VFIO_EEH_PE_OP: {
> + struct tce_iommu_group *tcegrp;
> +
> + ret = 0;
> + list_for_each_entry(tcegrp, &container->group_list, next) {
> + ret = vfio_spapr_iommu_eeh_ioctl(tcegrp->grp,
> + cmd, arg);
> + if (ret)
> + return ret;

Hrm. It occurs to me that EEH may need a way of referencing
individual groups. Even if multiple PEs are referencing the same TCE
tables, presumably EEH will isolate them individually.

> + }
> + return ret;
> + }
> +
> }
>
> return -ENOTTY;
> @@ -724,11 +808,14 @@ static void tce_iommu_release_ownership(struct tce_container *container,
> int i;
>
> for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> - struct iommu_table *tbl = &table_group->tables[i];
> + struct iommu_table *tbl = &container->tables[i];
>
> tce_iommu_clear(container, tbl, tbl->it_offset, tbl->it_size);
> if (tbl->it_map)
> iommu_release_ownership(tbl);
> +
> + /* Reset the container's copy of the table descriptor */
> + memset(tbl, 0, sizeof(*tbl));
> }
> }
>
> @@ -758,38 +845,56 @@ static int tce_iommu_take_ownership(struct iommu_table_group *table_group)
> static int tce_iommu_attach_group(void *iommu_data,
> struct iommu_group *iommu_group)
> {
> - int ret;
> + int ret, i;
> struct tce_container *container = iommu_data;
> struct iommu_table_group *table_group;
> + struct tce_iommu_group *tcegrp = NULL;
> + bool first_group = !tce_groups_attached(container);
>
> mutex_lock(&container->lock);
>
> /* pr_debug("tce_vfio: Attaching group #%u to iommu %p\n",
> iommu_group_id(iommu_group), iommu_group); */
> - if (container->grp) {
> - pr_warn("tce_vfio: Only one group per IOMMU container is allowed, existing id=%d, attaching id=%d\n",
> - iommu_group_id(container->grp),
> - iommu_group_id(iommu_group));
> - ret = -EBUSY;
> - goto unlock_exit;
> - }
> -
> - if (container->enabled) {
> - pr_err("tce_vfio: attaching group #%u to enabled container\n",
> - iommu_group_id(iommu_group));
> - ret = -EBUSY;
> - goto unlock_exit;
> - }
> -
> table_group = iommu_group_get_iommudata(iommu_group);
> - if (!table_group) {
> - ret = -ENXIO;
> +
> + if (!first_group && (!table_group->ops ||
> + !table_group->ops->take_ownership ||
> + !table_group->ops->release_ownership)) {
> + ret = -EBUSY;
> + goto unlock_exit;
> + }
> +
> + /* Check if new group has the same iommu_ops (i.e. compatible) */
> + list_for_each_entry(tcegrp, &container->group_list, next) {
> + struct iommu_table_group *table_group_tmp;
> +
> + if (tcegrp->grp == iommu_group) {
> + pr_warn("tce_vfio: Group %d is already attached\n",
> + iommu_group_id(iommu_group));
> + ret = -EBUSY;
> + goto unlock_exit;
> + }
> + table_group_tmp = iommu_group_get_iommudata(tcegrp->grp);
> + if (table_group_tmp->ops != table_group->ops) {
> + pr_warn("tce_vfio: Group %d is incompatible with group %d\n",
> + iommu_group_id(iommu_group),
> + iommu_group_id(tcegrp->grp));
> + ret = -EPERM;
> + goto unlock_exit;
> + }
> + }
> +
> + tcegrp = kzalloc(sizeof(*tcegrp), GFP_KERNEL);
> + if (!tcegrp) {
> + ret = -ENOMEM;
> goto unlock_exit;
> }
>
> if (!table_group->ops || !table_group->ops->take_ownership ||
> !table_group->ops->release_ownership) {
> ret = tce_iommu_take_ownership(table_group);
> + if (!ret)
> + container->tables[0] = table_group->tables[0];
> } else if (!table_group->ops->create_table ||
> !table_group->ops->set_window) {
> WARN_ON_ONCE(1);
> @@ -801,23 +906,46 @@ static int tce_iommu_attach_group(void *iommu_data,
> * the pages that has been explicitly mapped into the iommu
> */
> table_group->ops->take_ownership(table_group);
> - ret = table_group->ops->create_table(table_group,
> - 0, /* window number */
> - IOMMU_PAGE_SHIFT_4K,
> - table_group->tce32_size,
> - 1, /* default levels */
> - &table_group->tables[0]);
> - if (!ret)
> - ret = table_group->ops->set_window(table_group, 0,
> - &table_group->tables[0]);
> + /*
> + * If it the first group attached, check if there is
> + * a default DMA window and create one if none as
> + * the userspace expects it to exist.
> + */
> + if (first_group && !container->tables[0].it_size) {
> + ret = tce_iommu_create_table(table_group,
> + 0, /* window number */
> + IOMMU_PAGE_SHIFT_4K,
> + table_group->tce32_size,
> + 1, /* default levels */
> + &container->tables[0]);
> + if (ret)
> + goto unlock_exit;
> + }
> +
> + /* Set all windows to the new group */
> + for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> + struct iommu_table *tbl = &container->tables[i];
> +
> + if (!tbl->it_size)
> + continue;
> +
> + /* Set the default window to a new group */
> + ret = table_group->ops->set_window(table_group, i, tbl);
> + if (ret)
> + break;
> + }
> }
>
> if (ret)
> goto unlock_exit;
>
> - container->grp = iommu_group;
> + tcegrp->grp = iommu_group;
> + list_add(&tcegrp->next, &container->group_list);
>
> unlock_exit:
> + if (ret && tcegrp)
> + kfree(tcegrp);
> +
> mutex_unlock(&container->lock);
>
> return ret;
> @@ -828,25 +956,27 @@ static void tce_iommu_detach_group(void *iommu_data,
> {
> struct tce_container *container = iommu_data;
> struct iommu_table_group *table_group;
> + struct tce_iommu_group *tcegrp;
> long i;
> + bool found = false;
>
> mutex_lock(&container->lock);
> - if (iommu_group != container->grp) {
> - pr_warn("tce_vfio: detaching group #%u, expected group is #%u\n",
> - iommu_group_id(iommu_group),
> - iommu_group_id(container->grp));
> +
> + list_for_each_entry(tcegrp, &container->group_list, next) {
> + if (tcegrp->grp == iommu_group) {
> + found = true;
> + break;
> + }
> + }
> +
> + if (!found) {
> + pr_warn("tce_vfio: detaching unattached group #%u\n",
> + iommu_group_id(iommu_group));
> goto unlock_exit;
> }
>
> - if (container->enabled) {
> - pr_warn("tce_vfio: detaching group #%u from enabled container, forcing disable\n",
> - iommu_group_id(container->grp));
> - tce_iommu_disable(container);
> - }
> -
> - /* pr_debug("tce_vfio: detaching group #%u from iommu %p\n",
> - iommu_group_id(iommu_group), iommu_group); */
> - container->grp = NULL;
> + list_del(&tcegrp->next);
> + kfree(tcegrp);
>
> table_group = iommu_group_get_iommudata(iommu_group);
> BUG_ON(!table_group);
> @@ -857,18 +987,8 @@ static void tce_iommu_detach_group(void *iommu_data,
> else if (!table_group->ops->unset_window)
> WARN_ON_ONCE(1);
> else {
> - for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> - struct iommu_table tbl = table_group->tables[i];
> -
> - if (!tbl.it_size)
> - continue;
> -
> + for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i)
> table_group->ops->unset_window(table_group, i);
> - tce_iommu_clear(container, &tbl,
> - tbl.it_offset, tbl.it_size);
> - if (tbl.it_ops->free)
> - tbl.it_ops->free(&tbl);
> - }
>
> table_group->ops->release_ownership(table_group);
> }

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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