Re: [PATCH v3 1/2] vhost: Add rbtree vdpa_mem_tree to saved the counted mem

From: Jason Wang
Date: Tue Jun 28 2022 - 02:04:05 EST

On Tue, Jun 28, 2022 at 1:58 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Tue, Jun 28, 2022 at 11:54:27AM +0800, Jason Wang wrote:
> > On Mon, Jun 27, 2022 at 6:01 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> > >
> > > On Mon, Jun 27, 2022 at 04:12:57PM +0800, Cindy Lu wrote:
> > > > On Sun, Jun 26, 2022 at 6:01 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> > > > >
> > > > > On Sun, Jun 26, 2022 at 05:04:08PM +0800, Cindy Lu wrote:
> > > > > > We count pinned_vm as follow in vhost-vDPA
> > > > > >
> > > > > > lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> > > > > > if (npages + atomic64_read(&dev->mm->pinned_vm) > lock_limit) {
> > > > > > ret = -ENOMEM;
> > > > > > goto unlock;
> > > > > > }
> > > > > > This means if we have two vDPA devices for the same VM the pages
> > > > > > would be counted twice. So we add a tree to save the page that
> > > > > > counted and we will not count it again.
> > > > > >
> > > > > > Add vdpa_mem_tree to saved the mem that already counted.
> > > > > > use a hlist to saved the root for vdpa_mem_tree.
> > > > > >
> > > > > > Signed-off-by: Cindy Lu <lulu@xxxxxxxxxx>
> > > > > > ---
> > > > > > drivers/vhost/vhost.c | 63 +++++++++++++++++++++++++++++++++++++++++++
> > > > > > drivers/vhost/vhost.h | 1 +
> > > > > > 2 files changed, 64 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > > > > index 40097826cff0..4ca8b1ed944b 100644
> > > > > > --- a/drivers/vhost/vhost.c
> > > > > > +++ b/drivers/vhost/vhost.c
> > > > > > @@ -32,6 +32,8 @@
> > > > > > #include <linux/kcov.h>
> > > > > >
> > > > > > #include "vhost.h"
> > > > > > +#include <linux/hashtable.h>
> > > > > > +#include <linux/jhash.h>
> > > > > >
> > > > > > static ushort max_mem_regions = 64;
> > > > > > module_param(max_mem_regions, ushort, 0444);
> > > > > > @@ -49,6 +51,14 @@ enum {
> > > > > > #define vhost_used_event(vq) ((__virtio16 __user *)&vq->avail->ring[vq->num])
> > > > > > #define vhost_avail_event(vq) ((__virtio16 __user *)&vq->used->ring[vq->num])
> > > > > >
> > > > > > +struct vhost_vdpa_rbtree_node {
> > > > > > + struct hlist_node node;
> > > > > > + struct rb_root_cached vdpa_mem_tree;
> > > > > > + struct mm_struct *mm_using;
> > > > > > +};
> > > > > > +static DECLARE_HASHTABLE(vhost_vdpa_rbtree_hlist, 8);
> > > > > > +int vhost_vdpa_rbtree_hlist_status;
> > > > > > +
> > > > > > #ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
> > > > > > static void vhost_disable_cross_endian(struct vhost_virtqueue *vq)
> > > > > > {
> > > > >
> > > > > Are you trying to save some per-mm information here?
> > > > > Can't we just add it to mm_struct?
> > > > >
> > > > yes, this is a per-mm information, but I have checked with jason before,
> > > > seems it maybe difficult to change the mm_struct in upstream
> > > > so I add an to add a hlist instead
> > > > Thanks
> > > > Cindy
> > >
> > > Difficult how?
> >
> > It is only useful for vDPA probably. Though it could be used by VFIO
> > as well, VFIO does pinning/accounting at the container level and it
> > has been there for years.
>
> Yes it's been there, I'm not sure this means it's perfect.
> Also, rdma guys might be interested too I guess?

It looks to me they plan to go to iommufd as well.

>
> > vDPA have an implicit "container" the
> > mm_struct, but the accounting is done per device right now.
> >
> > In the future, when vDPA switches to iommufd, it can be then solved at
> > iommufd level.
>
> So is it even worth fixing now?

Not sure, but I guess it's better. (Or we need to teach the libvirt to
have special care on this).

>
> > And if we do this in mm, it will bring extra overheads.
> >
> > Thanks
>
> Pointer per mm, not too bad ...

Unless we enable it unconditionally, it requires a lot of tree
operations at least.

Thanks

>
> > > You get more scrutiny if you try, for sure,
> > > and you need to need to generalize it enough that it looks
> > > useful outside the driver. But I guess that's good?
> > >
> > > > >
> > > > >
> > > > > > @@ -571,6 +581,51 @@ static void vhost_detach_mm(struct vhost_dev *dev)
> > > > > > dev->mm = NULL;
> > > > > > }
> > > > > >
> > > > > > +struct rb_root_cached *vhost_vdpa_get_mem_tree(struct mm_struct *mm)
> > > > > > +{
> > > > > > + struct vhost_vdpa_rbtree_node *rbtree_root = NULL;
> > > > > > + struct rb_root_cached *vdpa_tree;
> > > > > > + u32 key;
> > > > > > +
> > > > > > + /* No hased table, init one */
> > > > > > + if (vhost_vdpa_rbtree_hlist_status == 0) {
> > > > > > + hash_init(vhost_vdpa_rbtree_hlist);
> > > > > > + vhost_vdpa_rbtree_hlist_status = 1;
> > > > > > + }
> > > > > > +
> > > > > > + key = jhash_1word((u64)mm, JHASH_INITVAL);
> > > > > > + hash_for_each_possible(vhost_vdpa_rbtree_hlist, rbtree_root, node,
> > > > > > + key) {
> > > > > > + if (rbtree_root->mm_using == mm)
> > > > > > + return &(rbtree_root->vdpa_mem_tree);
> > > > > > + }
> > > > > > + rbtree_root = kmalloc(sizeof(*rbtree_root), GFP_KERNEL);
> > > > > > + if (!rbtree_root)
> > > > > > + return NULL;
> > > > > > + rbtree_root->mm_using = mm;
> > > > > > + rbtree_root->vdpa_mem_tree = RB_ROOT_CACHED;
> > > > > > + hash_add(vhost_vdpa_rbtree_hlist, &rbtree_root->node, key);
> > > > > > + vdpa_tree = &(rbtree_root->vdpa_mem_tree);
> > > > > > + return vdpa_tree;
> > > > > > +}
> > > > > > +
> > > > > > +void vhost_vdpa_relase_mem_tree(struct mm_struct *mm)
> > > > > > +{
> > > > > > + struct vhost_vdpa_rbtree_node *rbtree_root = NULL;
> > > > > > + u32 key;
> > > > > > +
> > > > > > + key = jhash_1word((u64)mm, JHASH_INITVAL);
> > > > > > +
> > > > > > + /* No hased table, init one */
> > > > > > + hash_for_each_possible(vhost_vdpa_rbtree_hlist, rbtree_root, node,
> > > > > > + key) {
> > > > > > + if (rbtree_root->mm_using == mm) {
> > > > > > + hash_del(&rbtree_root->node);
> > > > > > + kfree(rbtree_root);
> > > > > > + }
> > > > > > + }
> > > > > > +}
> > > > > > +
> > > > > > /* Caller should have device mutex */
> > > > > > long vhost_dev_set_owner(struct vhost_dev *dev)
> > > > > > {
> > > > > > @@ -605,6 +660,11 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
> > > > > > err = vhost_dev_alloc_iovecs(dev);
> > > > > > if (err)
> > > > > > goto err_cgroup;
> > > > > > + dev->vdpa_mem_tree = vhost_vdpa_get_mem_tree(dev->mm);
> > > > > > + if (dev->vdpa_mem_tree == NULL) {
> > > > > > + err = -ENOMEM;
> > > > > > + goto err_cgroup;
> > > > > > + }
> > > > > >
> > > > > > return 0;
> > > > > > err_cgroup:
> > > > > > @@ -613,6 +673,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
> > > > > > dev->worker = NULL;
> > > > > > }
> > > > > > err_worker:
> > > > > > + vhost_vdpa_relase_mem_tree(dev->mm);
> > > > > > vhost_detach_mm(dev);
> > > > > > dev->kcov_handle = 0;
> > > > > > err_mm:
> > > > > > @@ -710,6 +771,8 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > > > > > dev->worker = NULL;
> > > > > > dev->kcov_handle = 0;
> > > > > > }
> > > > > > +
> > > > > > + vhost_vdpa_relase_mem_tree(dev->mm);
> > > > > > vhost_detach_mm(dev);
> > > > > > }
> > > > > > EXPORT_SYMBOL_GPL(vhost_dev_cleanup);
> > > > > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > > > > > index d9109107af08..84de33de3abf 100644
> > > > > > --- a/drivers/vhost/vhost.h
> > > > > > +++ b/drivers/vhost/vhost.h
> > > > > > @@ -160,6 +160,7 @@ struct vhost_dev {
> > > > > > int byte_weight;
> > > > > > u64 kcov_handle;
> > > > > > bool use_worker;
> > > > > > + struct rb_root_cached *vdpa_mem_tree;
> > > > > > int (*msg_handler)(struct vhost_dev *dev, u32 asid,
> > > > > > struct vhost_iotlb_msg *msg);
> > > > > > };
> > > > > > --
> > > > > > 2.34.3
> > > > >
> > >
>