[PATCH kernel v3 4/4] powerpc/mm/iommu, vfio/spapr: Put pages on VFIO container shutdown
David Gibson
david at gibson.dropbear.id.au
Fri Oct 21 11:29:33 AEDT 2016
On Thu, Oct 20, 2016 at 02:03:50PM +1100, Alexey Kardashevskiy wrote:
> At the moment the userspace tool is expected to request pinning of
> the entire guest RAM when VFIO IOMMU SPAPR v2 driver is present.
> When the userspace process finishes, all the pinned pages need to
> be put; this is done as a part of the userspace memory context (MM)
> destruction which happens on the very last mmdrop().
>
> This approach has a problem that a MM of the userspace process
> may live longer than the userspace process itself as kernel threads
> use userspace process MMs which was runnning on a CPU where
> the kernel thread was scheduled to. If this happened, the MM remains
> referenced until this exact kernel thread wakes up again
> and releases the very last reference to the MM, on an idle system this
> can take even hours.
>
> This moves preregistered regions tracking from MM to VFIO; insteads of
> using mm_iommu_table_group_mem_t::used, tce_container::prereg_list is
> added so each container releases regions which it has pre-registered.
>
> This changes the userspace interface to return EBUSY if a memory
> region is already registered in a container. However it should not
> have any practical effect as the only userspace tool available now
> does register memory region once per container anyway.
>
> As tce_iommu_register_pages/tce_iommu_unregister_pages are called
> under container->lock, this does not need additional locking.
>
> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
> Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> Changes:
> v3:
> * moved tce_iommu_prereg_free() call out of list_for_each_entry()
>
> v2:
> * updated commit log
> ---
> arch/powerpc/mm/mmu_context_book3s64.c | 4 ---
> arch/powerpc/mm/mmu_context_iommu.c | 11 --------
> drivers/vfio/vfio_iommu_spapr_tce.c | 49 +++++++++++++++++++++++++++++++++-
> 3 files changed, 48 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
> index ad82735..1a07969 100644
> --- a/arch/powerpc/mm/mmu_context_book3s64.c
> +++ b/arch/powerpc/mm/mmu_context_book3s64.c
> @@ -159,10 +159,6 @@ static inline void destroy_pagetable_page(struct mm_struct *mm)
>
> void destroy_context(struct mm_struct *mm)
> {
> -#ifdef CONFIG_SPAPR_TCE_IOMMU
> - mm_iommu_cleanup(mm);
> -#endif
> -
> #ifdef CONFIG_PPC_ICSWX
> drop_cop(mm->context.acop, mm);
> kfree(mm->context.cop_lockp);
> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> index 4c6db09..104bad0 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -365,14 +365,3 @@ void mm_iommu_init(struct mm_struct *mm)
> {
> INIT_LIST_HEAD_RCU(&mm->context.iommu_group_mem_list);
> }
> -
> -void mm_iommu_cleanup(struct mm_struct *mm)
> -{
> - struct mm_iommu_table_group_mem_t *mem, *tmp;
> -
> - list_for_each_entry_safe(mem, tmp, &mm->context.iommu_group_mem_list,
> - next) {
> - list_del_rcu(&mem->next);
> - mm_iommu_do_free(mem);
> - }
> -}
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 6b0b121..3e2f757 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -86,6 +86,15 @@ struct tce_iommu_group {
> };
>
> /*
> + * A container needs to remember which preregistered region it has
> + * referenced to do proper cleanup at the userspace process exit.
> + */
> +struct tce_iommu_prereg {
> + struct list_head next;
> + struct mm_iommu_table_group_mem_t *mem;
> +};
> +
> +/*
> * The container descriptor supports only a single group per container.
> * Required by the API as the container is not supplied with the IOMMU group
> * at the moment of initialization.
> @@ -98,12 +107,27 @@ struct tce_container {
> struct mm_struct *mm;
> struct iommu_table *tables[IOMMU_TABLE_GROUP_MAX_TABLES];
> struct list_head group_list;
> + struct list_head prereg_list;
> };
>
> +static long tce_iommu_prereg_free(struct tce_container *container,
> + struct tce_iommu_prereg *tcemem)
> +{
> + long ret;
> +
> + list_del(&tcemem->next);
> + ret = mm_iommu_put(container->mm, tcemem->mem);
> + kfree(tcemem);
> +
> + return ret;
> +}
> +
> static long tce_iommu_unregister_pages(struct tce_container *container,
> __u64 vaddr, __u64 size)
> {
> struct mm_iommu_table_group_mem_t *mem;
> + struct tce_iommu_prereg *tcemem;
> + bool found = false;
>
> if (!current || !current->mm)
> return -ESRCH; /* process exited */
> @@ -115,7 +139,17 @@ static long tce_iommu_unregister_pages(struct tce_container *container,
> if (!mem)
> return -ENOENT;
>
> - return mm_iommu_put(container->mm, mem);
> + list_for_each_entry(tcemem, &container->prereg_list, next) {
> + if (tcemem->mem == mem) {
> + found = true;
> + break;
> + }
> + }
> +
> + if (!found)
> + return -ENOENT;
> +
> + return tce_iommu_prereg_free(container, tcemem);
> }
>
> static long tce_iommu_register_pages(struct tce_container *container,
> @@ -123,6 +157,7 @@ static long tce_iommu_register_pages(struct tce_container *container,
> {
> long ret = 0;
> struct mm_iommu_table_group_mem_t *mem = NULL;
> + struct tce_iommu_prereg *tcemem;
> unsigned long entries = size >> PAGE_SHIFT;
>
> if (!current || !current->mm)
> @@ -136,6 +171,17 @@ static long tce_iommu_register_pages(struct tce_container *container,
> if (ret)
> return ret;
>
> + list_for_each_entry(tcemem, &container->prereg_list, next) {
> + if (tcemem->mem == mem) {
> + mm_iommu_put(container->mm, mem);
> + return -EBUSY;
> + }
> + }
Wouldn't it make more sense to do this duplicate check before the
mm_iommu_get(), so you don't have to roll it back on this error path.
> +
> + tcemem = kzalloc(sizeof(*tcemem), GFP_KERNEL);
> + tcemem->mem = mem;
> + list_add(&tcemem->next, &container->prereg_list);
> +
> container->enabled = true;
>
> return 0;
> @@ -320,6 +366,7 @@ static void *tce_iommu_open(unsigned long arg)
>
> mutex_init(&container->lock);
> INIT_LIST_HEAD_RCU(&container->group_list);
> + INIT_LIST_HEAD_RCU(&container->prereg_list);
>
> container->v2 = arg == VFIO_SPAPR_TCE_v2_IOMMU;
>
--
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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