Re: [PATCH v13 Kernel 7/7] vfio: Selective dirty page tracking if IOMMU backed device pins pages

[Alex Williamson]

On Tue, 17 Mar 2020 23:58:38 +0530
Kirti Wankhede <address@hidden> wrote:

> On 3/14/2020 2:19 AM, Alex Williamson wrote:
> > On Thu, 12 Mar 2020 23:23:27 +0530
> > Kirti Wankhede <address@hidden> wrote:
> >   
> >> Added a check such that only singleton IOMMU groups can pin pages.
> >>  From the point when vendor driver pins any pages, consider IOMMU group
> >> dirty page scope to be limited to pinned pages.
> >>
> >> To optimize to avoid walking list often, added flag
> >> pinned_page_dirty_scope to indicate if all of the vfio_groups for each
> >> vfio_domain in the domain_list dirty page scope is limited to pinned
> >> pages. This flag is updated on first pinned pages request for that IOMMU
> >> group and on attaching/detaching group.
> >>
> >> Signed-off-by: Kirti Wankhede <address@hidden>
> >> Reviewed-by: Neo Jia <address@hidden>
> >> ---
> >>   drivers/vfio/vfio.c             |  9 +++++-
> >>   drivers/vfio/vfio_iommu_type1.c | 72 
> >> +++++++++++++++++++++++++++++++++++++++--
> >>   include/linux/vfio.h            |  4 ++-
> >>   3 files changed, 80 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> >> index c8482624ca34..79108c1245a5 100644
> >> --- a/drivers/vfio/vfio.c
> >> +++ b/drivers/vfio/vfio.c
> >> @@ -85,6 +85,7 @@ struct vfio_group {
> >>    atomic_t                        opened;
> >>    wait_queue_head_t               container_q;
> >>    bool                            noiommu;
> >> +  unsigned int                    dev_counter;
> >>    struct kvm                      *kvm;
> >>    struct blocking_notifier_head   notifier;
> >>   };
> >> @@ -555,6 +556,7 @@ struct vfio_device *vfio_group_create_device(struct 
> >> vfio_group *group,
> >>   
> >>    mutex_lock(&group->device_lock);
> >>    list_add(&device->group_next, &group->device_list);
> >> +  group->dev_counter++;
> >>    mutex_unlock(&group->device_lock);
> >>   
> >>    return device;
> >> @@ -567,6 +569,7 @@ static void vfio_device_release(struct kref *kref)
> >>    struct vfio_group *group = device->group;
> >>   
> >>    list_del(&device->group_next);
> >> +  group->dev_counter--;
> >>    mutex_unlock(&group->device_lock);
> >>   
> >>    dev_set_drvdata(device->dev, NULL);
> >> @@ -1895,6 +1898,9 @@ int vfio_pin_pages(struct device *dev, unsigned long 
> >> *user_pfn, int npage,
> >>    if (!group)
> >>            return -ENODEV;
> >>   
> >> +  if (group->dev_counter > 1)
> >> +          return -EINVAL;
> >> +
> >>    ret = vfio_group_add_container_user(group);
> >>    if (ret)
> >>            goto err_pin_pages;
> >> @@ -1902,7 +1908,8 @@ int vfio_pin_pages(struct device *dev, unsigned long 
> >> *user_pfn, int npage,
> >>    container = group->container;
> >>    driver = container->iommu_driver;
> >>    if (likely(driver && driver->ops->pin_pages))
> >> -          ret = driver->ops->pin_pages(container->iommu_data, user_pfn,
> >> +          ret = driver->ops->pin_pages(container->iommu_data,
> >> +                                       group->iommu_group, user_pfn,
> >>                                         npage, prot, phys_pfn);
> >>    else
> >>            ret = -ENOTTY;
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c 
> >> b/drivers/vfio/vfio_iommu_type1.c
> >> index 4f1f116feabc..18a284b230c0 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -71,6 +71,7 @@ struct vfio_iommu {
> >>    bool                    v2;
> >>    bool                    nesting;
> >>    bool                    dirty_page_tracking;
> >> +  bool                    pinned_page_dirty_scope;
> >>   };
> >>   
> >>   struct vfio_domain {
> >> @@ -98,6 +99,7 @@ struct vfio_group {
> >>    struct iommu_group      *iommu_group;
> >>    struct list_head        next;
> >>    bool                    mdev_group;     /* An mdev group */
> >> +  bool                    has_pinned_pages;  
> > 
> > I'm afraid over time this name will be confusing, should we simply
> > call it pinned_page_dirty_scope per vfio_group as well?   
> 
> Updating as you suggested, but I hope it doesn't look confusing.
> 
> >  We might have
> > to adapt this over time as we get new ways to dirty pages, but each
> > group voting towards the same value being set on the vfio_iommu object
> > seems like a good starting point.
> >   
> >>   };
> >>   
> >>   struct vfio_iova {
> >> @@ -129,6 +131,10 @@ struct vfio_regions {
> >>   static int put_pfn(unsigned long pfn, int prot);
> >>   static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu);
> >>   
> >> +static struct vfio_group *vfio_iommu_find_iommu_group(struct vfio_iommu 
> >> *iommu,
> >> +                                         struct iommu_group *iommu_group);
> >> +
> >> +static void update_pinned_page_dirty_scope(struct vfio_iommu *iommu);
> >>   /*
> >>    * This code handles mapping and unmapping of user data buffers
> >>    * into DMA'ble space using the IOMMU
> >> @@ -579,11 +585,13 @@ static int vfio_unpin_page_external(struct vfio_dma 
> >> *dma, dma_addr_t iova,
> >>   }
> >>   
> >>   static int vfio_iommu_type1_pin_pages(void *iommu_data,
> >> +                                struct iommu_group *iommu_group,
> >>                                  unsigned long *user_pfn,
> >>                                  int npage, int prot,
> >>                                  unsigned long *phys_pfn)
> >>   {
> >>    struct vfio_iommu *iommu = iommu_data;
> >> +  struct vfio_group *group;
> >>    int i, j, ret;
> >>    unsigned long remote_vaddr;
> >>    struct vfio_dma *dma;
> >> @@ -662,8 +670,14 @@ static int vfio_iommu_type1_pin_pages(void 
> >> *iommu_data,
> >>                               (vpfn->iova - dma->iova) >> pgshift, 1);
> >>            }
> >>    }
> >> -
> >>    ret = i;
> >> +
> >> +  group = vfio_iommu_find_iommu_group(iommu, iommu_group);
> >> +  if (!group->has_pinned_pages) {
> >> +          group->has_pinned_pages = true;
> >> +          update_pinned_page_dirty_scope(iommu);
> >> +  }
> >> +
> >>    goto pin_done;
> >>   
> >>   pin_unwind:
> >> @@ -946,8 +960,11 @@ static int vfio_iova_dirty_bitmap(struct vfio_iommu 
> >> *iommu, dma_addr_t iova,
> >>    npages = dma->size >> pgshift;
> >>    bitmap_size = dirty_bitmap_bytes(npages);
> >>   
> >> -  /* mark all pages dirty if all pages are pinned and mapped. */
> >> -  if (dma->iommu_mapped)
> >> +  /*
> >> +   * mark all pages dirty if any IOMMU capable device is not able
> >> +   * to report dirty pages and all pages are pinned and mapped.
> >> +   */
> >> +  if (!iommu->pinned_page_dirty_scope && dma->iommu_mapped)
> >>            bitmap_set(dma->bitmap, 0, npages);
> >>   
> >>    if (dma->bitmap) {
> >> @@ -1430,6 +1447,51 @@ static struct vfio_group *find_iommu_group(struct 
> >> vfio_domain *domain,
> >>    return NULL;
> >>   }
> >>   
> >> +static struct vfio_group *vfio_iommu_find_iommu_group(struct vfio_iommu 
> >> *iommu,
> >> +                                         struct iommu_group *iommu_group)
> >> +{
> >> +  struct vfio_domain *domain;
> >> +  struct vfio_group *group = NULL;
> >> +
> >> +  list_for_each_entry(domain, &iommu->domain_list, next) {
> >> +          group = find_iommu_group(domain, iommu_group);
> >> +          if (group)
> >> +                  return group;
> >> +  }
> >> +
> >> +  if (iommu->external_domain)
> >> +          group = find_iommu_group(iommu->external_domain, iommu_group);
> >> +
> >> +  return group;
> >> +}
> >> +
> >> +static void update_pinned_page_dirty_scope(struct vfio_iommu *iommu)
> >> +{
> >> +  struct vfio_domain *domain;
> >> +  struct vfio_group *group;
> >> +
> >> +  list_for_each_entry(domain, &iommu->domain_list, next) {
> >> +          list_for_each_entry(group, &domain->group_list, next) {
> >> +                  if (!group->has_pinned_pages) {
> >> +                          iommu->pinned_page_dirty_scope = false;
> >> +                          return;
> >> +                  }
> >> +          }
> >> +  }
> >> +
> >> +  if (iommu->external_domain) {
> >> +          domain = iommu->external_domain;
> >> +          list_for_each_entry(group, &domain->group_list, next) {
> >> +                  if (!group->has_pinned_pages) {
> >> +                          iommu->pinned_page_dirty_scope = false;
> >> +                          return;
> >> +                  }
> >> +          }
> >> +  }
> >> +
> >> +  iommu->pinned_page_dirty_scope = true;
> >> +}
> >> +
> >>   static bool vfio_iommu_has_sw_msi(struct list_head *group_resv_regions,
> >>                              phys_addr_t *base)
> >>   {
> >> @@ -1836,6 +1898,7 @@ static int vfio_iommu_type1_attach_group(void 
> >> *iommu_data,
> >>   
> >>                    list_add(&group->next,
> >>                             &iommu->external_domain->group_list);
> >> +                  update_pinned_page_dirty_scope(iommu);
> >>                    mutex_unlock(&iommu->lock);
> >>   
> >>                    return 0;
> >> @@ -1958,6 +2021,7 @@ static int vfio_iommu_type1_attach_group(void 
> >> *iommu_data,
> >>   done:
> >>    /* Delete the old one and insert new iova list */
> >>    vfio_iommu_iova_insert_copy(iommu, &iova_copy);
> >> +  update_pinned_page_dirty_scope(iommu);
> >>    mutex_unlock(&iommu->lock);
> >>    vfio_iommu_resv_free(&group_resv_regions);
> >>     
> > 
> > At this point we've added an iommu backed group that can't possibly
> > have pages pinned on behalf of this group yet, can't we just set
> > iommu->pinned_page_dirty_scope = false?
> >   
> 
> Right, changing.
> 
> > In the previous case, aren't we adding a non-iommu backed group, so
> > should we presume the scope is pinned pages even before we have any?  
> 
> Anyways we are updating it when pages are pinned, I think better not to 
> presume.

If there's no iommu backing then the device doesn't have access to
dirty the pages itself, how else will they get dirty?  Perhaps I was a
little use in using the word "presume", I think there's a proof that
the pages must have limited dirty-scope.

> > We could almost forego the iommu scope update, but it could be the
> > first group added if we're going to preemptively assume the scope of
> > the group.
> >   
> >> @@ -1972,6 +2036,7 @@ static int vfio_iommu_type1_attach_group(void 
> >> *iommu_data,
> >>   out_free:
> >>    kfree(domain);
> >>    kfree(group);
> >> +  update_pinned_page_dirty_scope(iommu);  
> > 
> > This one looks like paranoia given how late we update when the group is
> > added.
> >   
> >>    mutex_unlock(&iommu->lock);
> >>    return ret;
> >>   }
> >> @@ -2176,6 +2241,7 @@ static void vfio_iommu_type1_detach_group(void 
> >> *iommu_data,
> >>            vfio_iommu_iova_free(&iova_copy);
> >>   
> >>   detach_group_done:
> >> +  update_pinned_page_dirty_scope(iommu);  
> > 
> > We only need to do this if the group we're removing does not have
> > pinned page dirty scope, right?  I think we have all the info here to
> > make that optimization.
> >   
> 
> There could be more than one group that doesn't have pinned page dirty 
> scope, better to run through update_pinned_page_dirty_scope() function.

Maybe I stated it wrong above, but I think we have this table:


iommu|group
-----+--------+---------+
XXXXX|   0    |    1    |
-----+--------+---------+
  0  |   A    |    B    |
-----+--------+---------+
  1  |   C    |    D    |
-----+--------+---------+

A: If we are NOT dirty-page-scope at the iommu and we remove a group
that is NOT dirty-page-scope, we need to check because that might have
been the group preventing the iommu from being dirty-page-scope.

B: If we are NOT dirty-page-scope at the iommu and we remove a group
that IS dirty-page-scope, we know that group wasn't limiting the scope
at the iommu.

C: If the iommu IS dirty-page-scope, we can't remove a group that is
NOT dirty page scope, this case is impossible.

D: If the iommu IS dirty-page-scope and we remove a group that IS dirty-
page-scope, nothing changes.

So I think we only need to update on A, or A+C since C cannot happen.
In B and D removing a group with dirt-page-scope cannot change the
iommu scope.  Thanks,

Alex

> >>    mutex_unlock(&iommu->lock);
> >>   }
> >>   
> >> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> >> index e42a711a2800..da29802d6276 100644
> >> --- a/include/linux/vfio.h
> >> +++ b/include/linux/vfio.h
> >> @@ -72,7 +72,9 @@ struct vfio_iommu_driver_ops {
> >>                                    struct iommu_group *group);
> >>    void            (*detach_group)(void *iommu_data,
> >>                                    struct iommu_group *group);
> >> -  int             (*pin_pages)(void *iommu_data, unsigned long *user_pfn,
> >> +  int             (*pin_pages)(void *iommu_data,
> >> +                               struct iommu_group *group,
> >> +                               unsigned long *user_pfn,
> >>                                 int npage, int prot,
> >>                                 unsigned long *phys_pfn);
> >>    int             (*unpin_pages)(void *iommu_data,  
> >   
>