Re: [PATCH v11 17/17]add two new ioctls for mp device.

Michael S. Tsirkin
2010-09-28T09:54:23Z

On Sat, Sep 25, 2010 at 12:27:35PM +0800, xiaohui.xin@intel.com wrote:
> From: Xin Xiaohui <xiaohui.xin@intel.com>
>
> The patch add two ioctls for mp device.
> One is for userspace to query how much memory locked to make mp device
> run smoothly. Another one is for userspace to set how much meory locked
> it really wants.
>
> ---
> drivers/vhost/mpassthru.c | 103 +++++++++++++++++++++++----------------------
> include/linux/mpassthru.h | 2 +
> 2 files changed, 54 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/vhost/mpassthru.c b/drivers/vhost/mpassthru.c
> index d86d94c..e3a0199 100644
> --- a/drivers/vhost/mpassthru.c
> +++ b/drivers/vhost/mpassthru.c
> @@ -67,6 +67,8 @@ static int debug;
> #define COPY_THRESHOLD (L1_CACHE_BYTES * 4)
> #define COPY_HDR_LEN (L1_CACHE_BYTES < 64 ? 64 : L1_CACHE_BYTES)
>
> +#define DEFAULT_NEED ((8192*2*2)*4096)
> +
> struct frag {
> u16 offset;
> u16 size;
> @@ -110,7 +112,8 @@ struct page_ctor {
> int rq_len;
> spinlock_t read_lock;

try documenting what fields are protected by which lock, btw.

> /* record the locked pages */
> - int lock_pages;
> + int locked_pages;
> + int cur_pages;
> struct rlimit o_rlim;

unused now?

> struct net_device *dev;
> struct mpassthru_port port;

This structure name should start with mp_ to avoid namespace pollution.
Also ctor implies a contructor function: see pgtable_page_ctor - it is
not a very good name for a structure.

> @@ -122,6 +125,7 @@ struct mp_struct {
> struct net_device *dev;
> struct page_ctor *ctor;
> struct socket socket;
> + struct task_struct *user;
>
> #ifdef MPASSTHRU_DEBUG
> int debug;
> @@ -231,7 +235,8 @@ static int page_ctor_attach(struct mp_struct *mp)
> ctor->port.ctor = page_ctor;
> ctor->port.sock = &mp->socket;
> ctor->port.hash = mp_lookup;
> - ctor->lock_pages = 0;
> + ctor->locked_pages = 0;
> + ctor->cur_pages = 0;
>
> /* locked by mp_mutex */
> dev->mp_port = &ctor->port;
> @@ -264,37 +269,6 @@ struct page_info *info_dequeue(struct page_ctor *ctor)
> return info;
> }
>
> -static int set_memlock_rlimit(struct page_ctor *ctor, int resource,
> - unsigned long cur, unsigned long max)
> -{
> - struct rlimit new_rlim, *old_rlim;
> - int retval;
> -
> - if (resource != RLIMIT_MEMLOCK)
> - return -EINVAL;
> - new_rlim.rlim_cur = cur;
> - new_rlim.rlim_max = max;
> -
> - old_rlim = current->signal->rlim + resource;
> -
> - /* remember the old rlimit value when backend enabled */
> - ctor->o_rlim.rlim_cur = old_rlim->rlim_cur;
> - ctor->o_rlim.rlim_max = old_rlim->rlim_max;
> -
> - if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
> - !capable(CAP_SYS_RESOURCE))
> - return -EPERM;
> -
> - retval = security_task_setrlimit(resource, &new_rlim);
> - if (retval)
> - return retval;
> -
> - task_lock(current->group_leader);
> - *old_rlim = new_rlim;
> - task_unlock(current->group_leader);
> - return 0;
> -}
> -
> static void relinquish_resource(struct page_ctor *ctor)
> {
> if (!(ctor->dev->flags & IFF_UP) &&
> @@ -323,7 +297,7 @@ static void mp_ki_dtor(struct kiocb *iocb)
> } else
> info->ctor->wq_len--;
> /* Decrement the number of locked pages */
> - info->ctor->lock_pages -= info->pnum;
> + info->ctor->cur_pages -= info->pnum;
> kmem_cache_free(ext_page_info_cache, info);
> relinquish_resource(info->ctor);
>
> @@ -357,6 +331,7 @@ static int page_ctor_detach(struct mp_struct *mp)
> {
> struct page_ctor *ctor;
> struct page_info *info;
> + struct task_struct *tsk = mp->user;
> int i;
>
> /* locked by mp_mutex */
> @@ -375,9 +350,9 @@ static int page_ctor_detach(struct mp_struct *mp)
>
> relinquish_resource(ctor);
>
> - set_memlock_rlimit(ctor, RLIMIT_MEMLOCK,
> - ctor->o_rlim.rlim_cur,
> - ctor->o_rlim.rlim_max);
> + down_write(&tsk->mm->mmap_sem);
> + tsk->mm->locked_vm -= ctor->locked_pages;
> + up_write(&tsk->mm->mmap_sem);
>
> /* locked by mp_mutex */
> ctor->dev->mp_port = NULL;
> @@ -514,7 +489,6 @@ static struct page_info *mp_hash_delete(struct page_ctor *ctor,
> {
> key_mp_t key = mp_hash(info->pages[0], HASH_BUCKETS);
> struct page_info *tmp = NULL;
> - int i;
>
> tmp = ctor->hash_table[key];
> while (tmp) {
> @@ -565,14 +539,11 @@ static struct page_info *alloc_page_info(struct page_ctor *ctor,
> int rc;
> int i, j, n = 0;
> int len;
> - unsigned long base, lock_limit;
> + unsigned long base;
> struct page_info *info = NULL;
>
> - lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
> - lock_limit >>= PAGE_SHIFT;
> -
> - if (ctor->lock_pages + count > lock_limit && npages) {
> - printk(KERN_INFO "exceed the locked memory rlimit.");
> + if (ctor->cur_pages + count > ctor->locked_pages) {
> + printk(KERN_INFO "Exceed memory lock rlimt.");
> return NULL;
> }
>
> @@ -634,7 +605,7 @@ static struct page_info *alloc_page_info(struct page_ctor *ctor,
> mp_hash_insert(ctor, info->pages[i], info);
> }
> /* increment the number of locked pages */
> - ctor->lock_pages += j;
> + ctor->cur_pages += j;
> return info;
>
> failed:
> @@ -1006,12 +977,6 @@ proceed:
> count--;
> }
>
> - if (!ctor->lock_pages || !ctor->rq_len) {
> - set_memlock_rlimit(ctor, RLIMIT_MEMLOCK,
> - iocb->ki_user_data * 4096 * 2,
> - iocb->ki_user_data * 4096 * 2);
> - }
> -
> /* Translate address to kernel */
> info = alloc_page_info(ctor, iocb, iov, count, frags, npages, 0);
> if (!info)
> @@ -1115,8 +1080,10 @@ static long mp_chr_ioctl(struct file *file, unsigned int cmd,
> struct mp_struct *mp;
> struct net_device *dev;
> void __user* argp = (void __user *)arg;
> + unsigned long __user *limitp = argp;
> struct ifreq ifr;
> struct sock *sk;
> + unsigned long limit, locked, lock_limit;
> int ret;
>
> ret = -EINVAL;
> @@ -1152,6 +1119,7 @@ static long mp_chr_ioctl(struct file *file, unsigned int cmd,
> goto err_dev_put;
> }
> mp->dev = dev;
> + mp->user = current;

This is unsafe: task might go away but fd will still exist.
You should get the mm like vhost does, then you can keep
a reference until release.

> ret = -ENOMEM;
>
> sk = sk_alloc(mfile->net, AF_UNSPEC, GFP_KERNEL, &mp_proto);
> @@ -1193,6 +1161,39 @@ err_dev_put:
> ret = do_unbind(mfile);
> break;
>
> + case MPASSTHRU_SET_MEM_LOCKED:
> + ret = copy_from_user(&limit, limitp, sizeof limit);
> + if (ret < 0)
> + return ret;
> +
> + mp = mp_get(mfile);
> + if (!mp)
> + return -ENODEV;
> +
> + limit = PAGE_ALIGN(limit) >> PAGE_SHIFT;
> + down_write(&current->mm->mmap_sem);

So here, current might be different from mp->user:
many processes might share an fd. The result
will be that you will subtract locked_vm from A but add it to B.

The right thing to do IMO is to store mm on SET_MEM_LOCKED.
Also be careful about multiple callers etc.

> + locked = limit + current->mm->locked_vm;
> + lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> +
> + if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) {
> + up_write(&current->mm->mmap_sem);
> + mp_put(mfile);
> + return -ENOMEM;
> + }
> + current->mm->locked_vm = locked;
> + up_write(&current->mm->mmap_sem);
> +
> + mutex_lock(&mp_mutex);
> + mp->ctor->locked_pages = limit;

What if a process calls SET_MEM_LOCKED multiple times
(or many processes do)? What if it is called when
some pages are already locked?
I suggested one way to handle that in one of the previous messages,
but you must think out these scenarious when you invent a new
ioctl.

> + mutex_unlock(&mp_mutex);
> +
> + mp_put(mfile);
> + return 0;
> +
> + case MPASSTHRU_GET_MEM_LOCKED_NEED:
> + limit = DEFAULT_NEED;
> + return copy_to_user(limitp, &limit, sizeof limit);
> +
> default:
> break;
> }
> diff --git a/include/linux/mpassthru.h b/include/linux/mpassthru.h
> index ba8f320..083e9f7 100644
> --- a/include/linux/mpassthru.h
> +++ b/include/linux/mpassthru.h
> @@ -7,6 +7,8 @@
> /* ioctl defines */
> #define MPASSTHRU_BINDDEV _IOW('M', 213, int)
> #define MPASSTHRU_UNBINDDEV _IO('M', 214)
> +#define MPASSTHRU_SET_MEM_LOCKED _IOW('M', 215, unsigned long)
> +#define MPASSTHRU_GET_MEM_LOCKED_NEED _IOR('M', 216, unsigned long)
>
> #ifdef __KERNEL__
> #if defined(CONFIG_MEDIATE_PASSTHRU) || defined(CONFIG_MEDIATE_PASSTHRU_MODULE)
> --
> 1.7.3
>
> --
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