On Sat, Aug 27, 2016 at 5:21 AM, Pavel Machek <pavel@xxxxxx> wrote: > > Hi! > >> Expose a new system call allowing each thread to register one userspace >> memory area to be used as an ABI between kernel and user-space for two >> purposes: user-space restartable sequences and quick access to read the >> current CPU number value from user-space. >> >> * Restartable sequences (per-cpu atomics) >> >> Restartables sequences allow user-space to perform update operations on >> per-cpu data without requiring heavy-weight atomic operations. >> >> The restartable critical sections (percpu atomics) work has been started >> by Paul Turner and Andrew Hunter. It lets the kernel handle restart of >> critical sections. [1] [2] The re-implementation proposed here brings a >> few simplifications to the ABI which facilitates porting to other >> architectures and speeds up the user-space fast path. A locking-based >> fall-back, purely implemented in user-space, is proposed here to deal >> with debugger single-stepping. This fallback interacts with rseq_start() >> and rseq_finish(), which force retries in response to concurrent >> lock-based activity. > > Hmm. Purely software fallback needed for singlestepping... Looks like this is malware > writer's dream come true... > > Also if you ever get bug in the restartable code, debugger will be useless to debug it... > unless new abilities are added to debuggers to manually schedule threads on CPUs. > > Is this good idea? We've had some off-list discussion. I have a revised version which incoprorates some of Mattheiu's improvements, but avoids this requirement nearly ready for posting. - Paul -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
