On Wed, Oct 12, 2016 at 03:58:28PM +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 <a...@ozlabs.ru> > Reviewed-by: Nicholas Piggin <npig...@gmail.com> > --- > Changes: > v2: > * updated commit log > --- > arch/powerpc/include/asm/mmu_context.h | 1 - > arch/powerpc/mm/mmu_context_book3s64.c | 4 --- > arch/powerpc/mm/mmu_context_iommu.c | 11 -------- > drivers/vfio/vfio_iommu_spapr_tce.c | 51 > +++++++++++++++++++++++++++++++++- > 4 files changed, 50 insertions(+), 17 deletions(-) > > diff --git a/arch/powerpc/include/asm/mmu_context.h > b/arch/powerpc/include/asm/mmu_context.h > index b9e3f0a..a6e18b5 100644 > --- a/arch/powerpc/include/asm/mmu_context.h > +++ b/arch/powerpc/include/asm/mmu_context.h > @@ -26,7 +26,6 @@ extern long mm_iommu_get(struct mm_struct *mm, > extern long mm_iommu_put(struct mm_struct *mm, > struct mm_iommu_table_group_mem_t *mem); > extern void mm_iommu_init(struct mm_struct *mm); > -extern void mm_iommu_cleanup(struct mm_struct *mm); > extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup(struct mm_struct > *mm, > unsigned long ua, unsigned long size); > extern struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm, > 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 3d2a65c..c8e9796 100644 > --- a/drivers/vfio/vfio_iommu_spapr_tce.c > +++ b/drivers/vfio/vfio_iommu_spapr_tce.c > @@ -89,6 +89,15 @@ 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. > @@ -101,12 +110,26 @@ 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; > > if ((vaddr & ~PAGE_MASK) || (size & ~PAGE_MASK)) > return -EINVAL; > @@ -115,7 +138,12 @@ 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) > + return tce_iommu_prereg_free(container, tcemem);
Hrm.. you're deleting tcemem from the list from within a list_for_each_entry (without _safe). It's probably not actually a use-after-free, because you return before hitting the next loop iteration, but that's pretty fragile and non-obvious. I think you'd be better using a break;, then doing the prereg_free() after the loop. > + } > + > + return -ENOENT; > } > > static long tce_iommu_register_pages(struct tce_container *container, > @@ -123,6 +151,7 @@ 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 ((vaddr & ~PAGE_MASK) || (size & ~PAGE_MASK) || > @@ -142,6 +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; > + } > + } > + > + tcemem = kzalloc(sizeof(*tcemem), GFP_KERNEL); > + tcemem->mem = mem; > + list_add(&tcemem->next, &container->prereg_list); > + > container->enabled = true; > > return 0; > @@ -327,6 +367,7 @@ 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; > > @@ -364,6 +405,14 @@ static void tce_iommu_release(void *iommu_data) > tce_iommu_free_table(tbl); > } > > + while (!list_empty(&container->prereg_list)) { > + struct tce_iommu_prereg *tcemem; > + > + tcemem = list_first_entry(&container->prereg_list, > + struct tce_iommu_prereg, next); > + tce_iommu_prereg_free(container, tcemem); > + } > + > if (container->mm) > mmdrop(container->mm); > tce_iommu_disable(container); -- 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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