Messages in this thread | | | Date | Mon, 09 Nov 2020 13:44:03 -0800 | From | si-wei liu <> | Subject | Re: [PATCH v2] vhost-vdpa: fix page pinning leakage in error path (rework) |
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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
> > 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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