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alex.williamson@redhat.com, mdf@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, cl@linux.com, hao.wu@intel.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 12/02/2019 09:44, Daniel Jordan wrote: > Beginning with bc3e53f682d9 ("mm: distinguish between mlocked and pinned > pages"), locked and pinned pages are accounted separately. The SPAPR > TCE VFIO IOMMU driver accounts pinned pages to locked_vm; use pinned_vm > instead. > > pinned_vm recently became atomic and so no longer relies on mmap_sem > held as writer: delete. > > Signed-off-by: Daniel Jordan > --- > Documentation/vfio.txt | 6 +-- > drivers/vfio/vfio_iommu_spapr_tce.c | 64 ++++++++++++++--------------- > 2 files changed, 33 insertions(+), 37 deletions(-) > > diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt > index f1a4d3c3ba0b..fa37d65363f9 100644 > --- a/Documentation/vfio.txt > +++ b/Documentation/vfio.txt > @@ -308,7 +308,7 @@ This implementation has some specifics: > currently there is no way to reduce the number of calls. In order to make > things faster, the map/unmap handling has been implemented in real mode > which provides an excellent performance which has limitations such as > - inability to do locked pages accounting in real time. > + inability to do pinned pages accounting in real time. > > 4) According to sPAPR specification, A Partitionable Endpoint (PE) is an I/O > subtree that can be treated as a unit for the purposes of partitioning and > @@ -324,7 +324,7 @@ This implementation has some specifics: > returns the size and the start of the DMA window on the PCI bus. > > VFIO_IOMMU_ENABLE > - enables the container. The locked pages accounting > + enables the container. The pinned pages accounting > is done at this point. This lets user first to know what > the DMA window is and adjust rlimit before doing any real job. > > @@ -454,7 +454,7 @@ This implementation has some specifics: > > PPC64 paravirtualized guests generate a lot of map/unmap requests, > and the handling of those includes pinning/unpinning pages and updating > - mm::locked_vm counter to make sure we do not exceed the rlimit. > + mm::pinned_vm counter to make sure we do not exceed the rlimit. > The v2 IOMMU splits accounting and pinning into separate operations: > > - VFIO_IOMMU_SPAPR_REGISTER_MEMORY/VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY ioctls > diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c > index c424913324e3..f47e020dc5e4 100644 > --- a/drivers/vfio/vfio_iommu_spapr_tce.c > +++ b/drivers/vfio/vfio_iommu_spapr_tce.c > @@ -34,9 +34,11 @@ > static void tce_iommu_detach_group(void *iommu_data, > struct iommu_group *iommu_group); > > -static long try_increment_locked_vm(struct mm_struct *mm, long npages) > +static long try_increment_pinned_vm(struct mm_struct *mm, long npages) > { > - long ret = 0, locked, lock_limit; > + long ret = 0; > + s64 pinned; > + unsigned long lock_limit; > > if (WARN_ON_ONCE(!mm)) > return -EPERM; > @@ -44,39 +46,33 @@ static long try_increment_locked_vm(struct mm_struct *mm, long npages) > if (!npages) > return 0; > > - down_write(&mm->mmap_sem); > - locked = mm->locked_vm + npages; > + pinned = atomic64_add_return(npages, &mm->pinned_vm); > lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; > - if (locked > lock_limit && !capable(CAP_IPC_LOCK)) > + if (pinned > lock_limit && !capable(CAP_IPC_LOCK)) { > ret = -ENOMEM; > - else > - mm->locked_vm += npages; > + atomic64_sub(npages, &mm->pinned_vm); > + } > > - pr_debug("[%d] RLIMIT_MEMLOCK +%ld %ld/%ld%s\n", current->pid, > + pr_debug("[%d] RLIMIT_MEMLOCK +%ld %ld/%lu%s\n", current->pid, > npages << PAGE_SHIFT, > - mm->locked_vm << PAGE_SHIFT, > - rlimit(RLIMIT_MEMLOCK), > - ret ? " - exceeded" : ""); > - > - up_write(&mm->mmap_sem); > + atomic64_read(&mm->pinned_vm) << PAGE_SHIFT, > + rlimit(RLIMIT_MEMLOCK), ret ? " - exceeded" : ""); > > return ret; > } > > -static void decrement_locked_vm(struct mm_struct *mm, long npages) > +static void decrement_pinned_vm(struct mm_struct *mm, long npages) > { > if (!mm || !npages) > return; > > - down_write(&mm->mmap_sem); > - if (WARN_ON_ONCE(npages > mm->locked_vm)) > - npages = mm->locked_vm; > - mm->locked_vm -= npages; > - pr_debug("[%d] RLIMIT_MEMLOCK -%ld %ld/%ld\n", current->pid, > + if (WARN_ON_ONCE(npages > atomic64_read(&mm->pinned_vm))) > + npages = atomic64_read(&mm->pinned_vm); > + atomic64_sub(npages, &mm->pinned_vm); > + pr_debug("[%d] RLIMIT_MEMLOCK -%ld %ld/%lu\n", current->pid, > npages << PAGE_SHIFT, > - mm->locked_vm << PAGE_SHIFT, > + atomic64_read(&mm->pinned_vm) << PAGE_SHIFT, > rlimit(RLIMIT_MEMLOCK)); > - up_write(&mm->mmap_sem); So it used to be down_write+up_write and stuff in between. Now it is 3 independent accesses (actually 4 but the last one is diagnostic) with no locking around them. Why do not we need a lock anymore precisely? Thanks, > } > > /* > @@ -110,7 +106,7 @@ struct tce_container { > bool enabled; > bool v2; > bool def_window_pending; > - unsigned long locked_pages; > + unsigned long pinned_pages; > struct mm_struct *mm; > struct iommu_table *tables[IOMMU_TABLE_GROUP_MAX_TABLES]; > struct list_head group_list; > @@ -283,7 +279,7 @@ static int tce_iommu_find_free_table(struct tce_container *container) > static int tce_iommu_enable(struct tce_container *container) > { > int ret = 0; > - unsigned long locked; > + unsigned long pinned; > struct iommu_table_group *table_group; > struct tce_iommu_group *tcegrp; > > @@ -292,15 +288,15 @@ static int tce_iommu_enable(struct tce_container *container) > > /* > * When userspace pages are mapped into the IOMMU, they are effectively > - * locked memory, so, theoretically, we need to update the accounting > - * of locked pages on each map and unmap. For powerpc, the map unmap > + * pinned memory, so, theoretically, we need to update the accounting > + * of pinned pages on each map and unmap. For powerpc, the map unmap > * paths can be very hot, though, and the accounting would kill > * performance, especially since it would be difficult to impossible > * to handle the accounting in real mode only. > * > * To address that, rather than precisely accounting every page, we > - * instead account for a worst case on locked memory when the iommu is > - * enabled and disabled. The worst case upper bound on locked memory > + * instead account for a worst case on pinned memory when the iommu is > + * enabled and disabled. The worst case upper bound on pinned memory > * is the size of the whole iommu window, which is usually relatively > * small (compared to total memory sizes) on POWER hardware. > * > @@ -317,7 +313,7 @@ static int tce_iommu_enable(struct tce_container *container) > * > * So we do not allow enabling a container without a group attached > * as there is no way to know how much we should increment > - * the locked_vm counter. > + * the pinned_vm counter. > */ > if (!tce_groups_attached(container)) > return -ENODEV; > @@ -335,12 +331,12 @@ static int tce_iommu_enable(struct tce_container *container) > if (ret) > return ret; > > - locked = table_group->tce32_size >> PAGE_SHIFT; > - ret = try_increment_locked_vm(container->mm, locked); > + pinned = table_group->tce32_size >> PAGE_SHIFT; > + ret = try_increment_pinned_vm(container->mm, pinned); > if (ret) > return ret; > > - container->locked_pages = locked; > + container->pinned_pages = pinned; > > container->enabled = true; > > @@ -355,7 +351,7 @@ static void tce_iommu_disable(struct tce_container *container) > container->enabled = false; > > BUG_ON(!container->mm); > - decrement_locked_vm(container->mm, container->locked_pages); > + decrement_pinned_vm(container->mm, container->pinned_pages); > } > > static void *tce_iommu_open(unsigned long arg) > @@ -658,7 +654,7 @@ static long tce_iommu_create_table(struct tce_container *container, > if (!table_size) > return -EINVAL; > > - ret = try_increment_locked_vm(container->mm, table_size >> PAGE_SHIFT); > + ret = try_increment_pinned_vm(container->mm, table_size >> PAGE_SHIFT); > if (ret) > return ret; > > @@ -677,7 +673,7 @@ static void tce_iommu_free_table(struct tce_container *container, > unsigned long pages = tbl->it_allocated_size >> PAGE_SHIFT; > > iommu_tce_table_put(tbl); > - decrement_locked_vm(container->mm, pages); > + decrement_pinned_vm(container->mm, pages); > } > > static long tce_iommu_create_window(struct tce_container *container, > -- Alexey