Messages in this thread | | | Date | Mon, 09 Nov 2020 15:56:21 -0800 | From | si-wei liu <> | Subject | Re: [PATCH v2] vhost-vdpa: fix page pinning leakage in error path (rework) |
| |
On 11/9/2020 2:42 PM, Michael S. Tsirkin wrote: > On Mon, Nov 09, 2020 at 01:44:03PM -0800, si-wei liu wrote: >> On 11/8/2020 7:21 PM, Jason Wang wrote: >>> On 2020/11/6 上午6:57, si-wei liu wrote: >>>> On 11/4/2020 7:26 PM, Jason Wang wrote: >>>>> On 2020/11/5 上午7:33, 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> >>>>>> --- >>>>>> Changes in v2: >>>>>> - Drop the reversion patch >>>>>> - Fix unhandled page leak towards the end of page_list >>>>>> >>>>>> drivers/vhost/vdpa.c | 79 >>>>>> ++++++++++++++++++++++++++++++++++++++++------------ >>>>>> 1 file changed, 61 insertions(+), 18 deletions(-) >>>>>> >>>>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c >>>>>> index b6d9016..e112854 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 +611,75 @@ 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) { >>>>>> + /* >>>>>> + * Unpin the pages that are left unmapped >>>>>> + * from this point on in the current >>>>>> + * page_list. The remaining outstanding >>>>>> + * ones which may stride across several >>>>>> + * chunks will be covered in the common >>>>>> + * error path subsequently. >>>>>> + */ >>>>>> + unpin_user_pages(&page_list[i], >>>>>> + pinned - i); >>>>> >>>>> Can we simply do last_pfn = this_pfn here? >>>> Nope. They are not contiguous segments of memory. Noted the >>>> conditional (this_pfn != last_pfn + 1) being held here. >>> >>> Right. >>> >>> >>>>> >>>>>> 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 +687,26 @@ static int >>>>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v, >>>>>> map_pfn << PAGE_SHIFT, msg->perm); >>>>>> out: >>>>>> if (ret) { >>>>>> + if (nchunks && last_pfn) { >>>>> >>>>> Any reason for checking last_pfn here? >>>>> >>>>> Note that we did: >>>>> >>>>> + nchunks++; >>>>> >>>>> if (!last_pfn) >>>>> map_pfn = page_to_pfn(page_list[0]); >>>> It's for explicit coding to make sure this common error path can be >>>> reused no matter if last_pfn has a sane value assigned or not. I can >>>> change it to an implicit WARN_ON() if need be. >>> >>> Just to make sure I understand. A question, when will we get nchunks != >>> 0 but last_pfn == 0? >> The current code has implicit assumption that nchunks != 0 infers last_pfn >> != 0. However, this assumption could break subject to code structure changes >> for eg. failure may occur after the increment of nchunks and before the for >> loop. I feel it'd be the best to capture this assumption with something >> explicit. >> >> -Siwei > if here isn't really an explicit way to document assumptions, > it's a way to avoid assumptions :) Agreed. I was referring to the v3 patch which had turned the defensive coding to a WARN_ON().
> A way to document assumptions is probably BUG_ON. If you're fine with below checkpatch warning I can definitely convert it to a BUG_ON:
WARNING: Avoid crashing the kernel - try using WARN_ON & recovery code rather than BUG() or BUG_ON()
Let me know if I need to post a v4 for this nit.
Thanks -Siwei
> >>> Thanks >>> >>> >>>> Thanks, >>>> -Siwei >>>> >>>>> >>>>> Thanks >>>>> >>>>> >>>>>> + unsigned long pfn; >>>>>> + >>>>>> + /* >>>>>> + * Unpin the outstanding pages which are yet to be >>>>>> + * mapped but haven't due to vdpa_map() or >>>>>> + * pin_user_pages() failure. >>>>>> + * >>>>>> + * Mapped pages are accounted in vdpa_map(), hence >>>>>> + * the corresponding unpinning 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); >>>>>> - atomic64_sub(npages, &dev->mm->pinned_vm); >>>>>> } >>>>>> +unlock: >>>>>> mmap_read_unlock(dev->mm); >>>>>> +free: >>>>>> free_page((unsigned long)page_list); >>>>>> return ret; >>>>>> }
| |