Messages in this thread | | | Date | Tue, 03 Nov 2020 18:14:08 -0800 | From | si-wei liu <> | Subject | Re: [PATCH 2/2] vhost-vdpa: fix page pinning leakage in error path (rework) |
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On 11/3/2020 5:58 PM, Jason Wang wrote: > > On 2020/11/4 上午9:08, si-wei liu wrote: >> >> On 11/3/2020 5:06 PM, si-wei liu wrote: >>> >>> On 11/3/2020 5:00 AM, Jason Wang wrote: >>>> >>>> On 2020/10/30 下午3:45, Si-Wei Liu wrote: >>>>> Pinned pages are not properly accounted particularly when >>>>> mapping error occurs on IOTLB update. Clean up dangling >>>>> pinned pages for the error path. >>>>> >>>>> The memory usage for bookkeeping pinned pages is reverted >>>>> to what it was before: only one single free page is needed. >>>>> This helps reduce the host memory demand for VM with a large >>>>> amount of memory, or in the situation where host is running >>>>> short of free memory. >>>>> >>>>> Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend") >>>>> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com> >>>>> --- >>>>> drivers/vhost/vdpa.c | 64 >>>>> +++++++++++++++++++++++++++++++++++++--------------- >>>>> 1 file changed, 46 insertions(+), 18 deletions(-) >>>>> >>>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c >>>>> index b6d9016..8da8558 100644 >>>>> --- a/drivers/vhost/vdpa.c >>>>> +++ b/drivers/vhost/vdpa.c >>>>> @@ -560,6 +560,8 @@ static int vhost_vdpa_map(struct vhost_vdpa *v, >>>>> if (r) >>>>> vhost_iotlb_del_range(dev->iotlb, iova, iova + size - 1); >>>>> + else >>>>> + atomic64_add(size >> PAGE_SHIFT, &dev->mm->pinned_vm); >>>>> return r; >>>>> } >>>>> @@ -591,14 +593,16 @@ static int >>>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v, >>>>> unsigned long list_size = PAGE_SIZE / sizeof(struct page *); >>>>> unsigned int gup_flags = FOLL_LONGTERM; >>>>> unsigned long npages, cur_base, map_pfn, last_pfn = 0; >>>>> - unsigned long locked, lock_limit, pinned, i; >>>>> + unsigned long lock_limit, sz2pin, nchunks, i; >>>>> u64 iova = msg->iova; >>>>> + long pinned; >>>>> int ret = 0; >>>>> if (vhost_iotlb_itree_first(iotlb, msg->iova, >>>>> msg->iova + msg->size - 1)) >>>>> return -EEXIST; >>>>> + /* Limit the use of memory for bookkeeping */ >>>>> page_list = (struct page **) __get_free_page(GFP_KERNEL); >>>>> if (!page_list) >>>>> return -ENOMEM; >>>>> @@ -607,52 +611,64 @@ static int >>>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v, >>>>> gup_flags |= FOLL_WRITE; >>>>> npages = PAGE_ALIGN(msg->size + (iova & ~PAGE_MASK)) >> >>>>> PAGE_SHIFT; >>>>> - if (!npages) >>>>> - return -EINVAL; >>>>> + if (!npages) { >>>>> + ret = -EINVAL; >>>>> + goto free; >>>>> + } >>>>> mmap_read_lock(dev->mm); >>>>> - locked = atomic64_add_return(npages, &dev->mm->pinned_vm); >>>>> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; >>>>> - >>>>> - if (locked > lock_limit) { >>>>> + if (npages + atomic64_read(&dev->mm->pinned_vm) > lock_limit) { >>>>> ret = -ENOMEM; >>>>> - goto out; >>>>> + goto unlock; >>>>> } >>>>> cur_base = msg->uaddr & PAGE_MASK; >>>>> iova &= PAGE_MASK; >>>>> + nchunks = 0; >>>>> while (npages) { >>>>> - pinned = min_t(unsigned long, npages, list_size); >>>>> - ret = pin_user_pages(cur_base, pinned, >>>>> - gup_flags, page_list, NULL); >>>>> - if (ret != pinned) >>>>> + sz2pin = min_t(unsigned long, npages, list_size); >>>>> + pinned = pin_user_pages(cur_base, sz2pin, >>>>> + gup_flags, page_list, NULL); >>>>> + if (sz2pin != pinned) { >>>>> + if (pinned < 0) { >>>>> + ret = pinned; >>>>> + } else { >>>>> + unpin_user_pages(page_list, pinned); >>>>> + ret = -ENOMEM; >>>>> + } >>>>> goto out; >>>>> + } >>>>> + nchunks++; >>>>> if (!last_pfn) >>>>> map_pfn = page_to_pfn(page_list[0]); >>>>> - for (i = 0; i < ret; i++) { >>>>> + for (i = 0; i < pinned; i++) { >>>>> unsigned long this_pfn = page_to_pfn(page_list[i]); >>>>> u64 csize; >>>>> if (last_pfn && (this_pfn != last_pfn + 1)) { >>>>> /* Pin a contiguous chunk of memory */ >>>>> csize = (last_pfn - map_pfn + 1) << PAGE_SHIFT; >>>>> - if (vhost_vdpa_map(v, iova, csize, >>>>> - map_pfn << PAGE_SHIFT, >>>>> - msg->perm)) >>>>> + ret = vhost_vdpa_map(v, iova, csize, >>>>> + map_pfn << PAGE_SHIFT, >>>>> + msg->perm); >>>>> + if (ret) >>>>> goto out; >>>>> + >>>>> map_pfn = this_pfn; >>>>> iova += csize; >>>>> + nchunks = 0; >>>>> } >>>>> last_pfn = this_pfn; >>>>> } >>>>> - cur_base += ret << PAGE_SHIFT; >>>>> - npages -= ret; >>>>> + cur_base += pinned << PAGE_SHIFT; >>>>> + npages -= pinned; >>>>> } >>>>> /* Pin the rest chunk */ >>>>> @@ -660,10 +676,22 @@ static int >>>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v, >>>>> map_pfn << PAGE_SHIFT, msg->perm); >>>>> out: >>>>> if (ret) { >>>>> + if (nchunks && last_pfn) { >>>>> + unsigned long pfn; >>>>> + >>>>> + /* >>>>> + * Unpin the outstanding pages which are unmapped. >>>>> + * Mapped pages are accounted in vdpa_map(), thus >>>>> + * will be handled by vdpa_unmap(). >>>>> + */ >>>>> + for (pfn = map_pfn; pfn <= last_pfn; pfn++) >>>>> + unpin_user_page(pfn_to_page(pfn)); >>>>> + } >>>>> vhost_vdpa_unmap(v, msg->iova, msg->size); >>>> >>>> >>>> I want to know what's wrong with current code. >>>> >>>> We call vhost_vdpa_unmap() on error which calls >>>> vhost_vdpa_iotlb_unmap() that will unpin and reduce the pinned_vm. >>> Think about the case where vhost_vdpa_map() fails in the middle >>> after making a few successful ones. In the current code, the >>> vhost_vdpa_iotlb_unmap() unpins what had been mapped, but does not >>> unpin those that have not yet been mapped. These outstanding pinned >>> pages will be leaked after leaving the vhost_vdpa_map() function. >> Typo: ... leaving the vhost_vdpa_process_iotlb_update() function. >>> >>> Also, the subtraction accounting at the end of the function is >>> incorrect in that case: @npages is deduced by @pinned in each >>> iteration. That's why I moved the accounting to vhost_vdpa_map() to >>> be symmetric with vhost_vdpa_unmap(). >>> > > I see, then I wonder if it would have more easy to read code if we do > (un)pinning/accouting only in vhost_vdpa_map()/vhost_vdpa_unmap()?
Yes. That's what I've done in my new code. Though, the caller still has to unpin the outstanding pages that aren't accounted for in vhost_vdpa_map().
-Siwei
> > Thanks > > >>> >>> -Siwei >>>> >>>> Thanks >>>> >>>> >>>>> - atomic64_sub(npages, &dev->mm->pinned_vm); >>>>> } >>>>> +unlock: >>>>> mmap_read_unlock(dev->mm); >>>>> +free: >>>>> free_page((unsigned long)page_list); >>>>> return ret; >>>>> } >>>> >>> >> >
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