On 4/2/25 8:34 AM, Dmitry Osipenko wrote: > On 4/2/25 04:53, Huang, Honglei1 wrote: >> >> On 2025/3/30 19:57, Dmitry Osipenko wrote: >>> If the purpose of this feature is to dedup usrptr BOs of a the single >>> process/application, can this can be done in userspace? > > I assume it can be done in userspace, don't see why it needs to be in > kernel.
The kernel definitely does not need to be responsible for deduplication, but is it safe to allow userspace to create overlapping BOs, especially ones that are partially but not entirely overlapping? If the userspace libraries ~everyone will be using refuse to create such BOs, then overlapping BOs will be tested by ~nobody, and untested kernel code is a good place for security vulnerabilities to linger. If there are no legitimate use-cases for overlapping BOs, I would treat attempts to create them as an errors and return -EINVAL, indicating that the userspace code attempting to create them is buggy. Userspace can deduplicate the BOs itself if necessary. Of course, there need to be tests for userspace attempting to create overlapping BOs, including attempting to do so concurrently from multiple threads. That said, probably the most important part is consistency with userptr in other (non-virtio) drivers, such as Intel and AMD. If they allow overlapping userptr BOs, then virtio should too; if they do not, then virtio should also forbid them. -- Sincerely, Demi Marie Obenour (she/her/hers)
