Messages in this thread | | | Subject | Re: [PATCH v2] vhost-vdpa: fix page pinning leakage in error path (rework) | From | Jason Wang <> | Date | Tue, 10 Nov 2020 11:27:42 +0800 |
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On 2020/11/10 上午7:56, si-wei liu wrote: > > 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().
I think I get you now.
> >> 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.
I will ack for V3.
Thanks
> > 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; >>>>>>> } >
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