On 22.03.23 15:55, Lorenzo Stoakes wrote:
Having previously laid the foundation for converting vread() to an iterator function, pull the trigger and do so. This patch attempts to provide minimal refactoring and to reflect the existing logic as best we can, for example we continue to zero portions of memory not read, as before. Overall, there should be no functional difference other than a performance improvement in /proc/kcore access to vmalloc regions. Now we have eliminated the need for a bounce buffer in read_kcore_iter(), we dispense with it, and try to write to user memory optimistically but with faults disabled via copy_page_to_iter_nofault(). We already have preemption disabled by holding a spin lock. If this fails, we fault in and retry a single time. This is a conservative approach intended to avoid spinning on vread_iter() if we repeatedly encouter issues reading from it.
I have to ask again: Can you comment why that is ok? You might end up signaling -EFAULT to user space simply because swapping/page migration/whatever triggered at the wrong time.
That could break existing user space or which important part am I missing? -- Thanks, David / dhildenb
