Messages in this thread Patch in this message | | | Date | Thu, 05 Nov 2020 14:40:12 -0800 | From | si-wei liu <> | Subject | Re: [PATCH 2/2] vhost-vdpa: fix page pinning leakage in error path (rework) |
| |
On 11/4/2020 7:12 PM, Jason Wang wrote: > > On 2020/11/5 上午7:40, si-wei liu wrote: >> >> On 11/3/2020 6:42 PM, 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) { >>> >>> >>> Can we decrease npages where you did "nchunks++" then we can check >>> npages here instead? >> Hmmm, I am not sure I get what you want... @nchunks gets reset to 0 >> whenever a certain range of pinned pages is successfully mapped. The >> conditional (when nchunks is non-zero) here indicates if there's any >> _outstanding_ pinned page that has to clean up in the error handling >> path. While the decrement of @npages may not occur when resetting the >> @nchunks counter, rendering incorrect cleanup in the error path. > > > Yes, I meant e can decrease npages where you did "nchunks++". Anyhow, > it's just a optimization to avoid a local variable which is not a must.
To me that opportunity doesn't exist. @nchunks and @npages track different kind of things. @npages is not interchangeable to represent all possible error cases.
-Siwei
> > >> >> BTW while reviewing it I got noticed of an error in my code. There >> might be still page pinning leak from wherever the vhost_vdpa_map() >> error occurs towards the end of page_list. I will post a v2 to fix this. >> > > Sure, will review. > > Thanks > > >> Regards, >> -Siwei >> >> --- a/drivers/vhost/vdpa.c >> +++ b/drivers/vhost/vdpa.c >> @@ -656,8 +656,19 @@ static int >> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v, >> ret = vhost_vdpa_map(v, iova, csize, >> map_pfn << >> PAGE_SHIFT, >> msg->perm); >> - if (ret) >> + 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); >> goto out; >> + } >> >> map_pfn = this_pfn; >> iova += csize; >> >> >> >>> >>> Thanks >>> >>> >>>> + 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); >>>> - atomic64_sub(npages, &dev->mm->pinned_vm); >>>> } >>>> +unlock: >>>> mmap_read_unlock(dev->mm); >>>> +free: >>>> free_page((unsigned long)page_list); >>>> return ret; >>>> } >>> >> >
| |