----- On Nov 6, 2017, at 8:24 PM, Boqun Feng boqun.f...@gmail.com wrote:
> On Mon, Nov 06, 2017 at 03:56:31PM -0500, Mathieu Desnoyers wrote:
> [...]
>> +
>> +/*
>> + * struct rseq is aligned on 4 * 8 bytes to ensure it is always
>> + * contained within a single cache-line.
>> + *
>> + * A single struct rseq per thread is allowed.
>> + */
>> +struct rseq {
>> + /*
>> + * Restartable sequences cpu_id_start field. Updated by the
>> + * kernel, and read by user-space with single-copy atomicity
>> + * semantics. Aligned on 32-bit. Always contain a value in the
>> + * range of possible CPUs, although the value may not be the
>> + * actual current CPU (e.g. if rseq is not initialized). This
>> + * CPU number value should always be confirmed against the value
>> + * of the cpu_id field.
>> + */
>> + uint32_t cpu_id_start;
>> + /*
>> + * Restartable sequences cpu_id field. Updated by the kernel,
>> + * and read by user-space with single-copy atomicity semantics.
>> + * Aligned on 32-bit. Values -1U and -2U have a special
>> + * semantic: -1U means "rseq uninitialized", and -2U means "rseq
>> + * initialization failed".
>> + */
>> + uint32_t cpu_id;
>> + /*
>> + * Restartable sequences rseq_cs field.
>> + *
>> + * Contains NULL when no critical section is active for the current
>> + * thread, or holds a pointer to the currently active struct rseq_cs.
>> + *
>> + * Updated by user-space at the beginning of assembly instruction
>> + * sequence block, and by the kernel when it restarts an assembly
>> + * instruction sequence block, and when the kernel detects that it
>> + * is preempting or delivering a signal outside of the range
>> + * targeted by the rseq_cs. Also needs to be cleared by user-space
>> + * before reclaiming memory that contains the targeted struct
>> + * rseq_cs.
>> + *
>> + * Read and set by the kernel with single-copy atomicity semantics.
>> + * Aligned on 64-bit.
>> + */
>> + RSEQ_FIELD_u32_u64(rseq_cs);
>> + /*
>> + * - RSEQ_DISABLE flag:
>> + *
>> + * Fallback fast-track flag for single-stepping.
>> + * Set by user-space if lack of progress is detected.
>> + * Cleared by user-space after rseq finish.
>> + * Read by the kernel.
>> + * - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT
>> + * Inhibit instruction sequence block restart and event
>> + * counter increment on preemption for this thread.
>
> Nit: "event counter" has been removed entirely ;-)
>
>> + * - RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL
>> + * Inhibit instruction sequence block restart and event
>> + * counter increment on signal delivery for this thread.
>> + * - RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
>> + * Inhibit instruction sequence block restart and event
>> + * counter increment on migration for this thread.
>> + */
>> + uint32_t flags;
>> +} __attribute__((aligned(4 * sizeof(uint64_t))));
>> +
>> +#endif /* _UAPI_LINUX_RSEQ_H */
> [...]
>> + } else {
>> + /*
>> + * If there was no rseq previously registered,
>> + * we need to ensure the provided rseq is
>> + * properly aligned and valid.
>> + */
>> + if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq))
>> + || rseq_len != sizeof(*rseq))
>> + return -EINVAL;
>> + if (!access_ok(VERIFY_WRITE, rseq, rseq_len))
>> + return -EFAULT;
>> + current->rseq = rseq;
>> + current->rseq_len = rseq_len;
>> + current->rseq_sig = sig;
>> + /*
>> + * If rseq was previously inactive, and has just
>> + * been registered, ensure the cpu_id and
>> + * event_counter fields are updated before
>
> s/event_counter/cpu_start_id/ ?
I guess you mean "cpu_id_start".
Good point. v11 will include that fix. Meanwhile, it is available
at
https://git.kernel.org/pub/scm/linux/kernel/git/rseq/linux-rseq.git/log/?h=rseq/dev
Thanks,
Mathieu
>
> Regards,
> Boqun
>
>> + * returning to user-space.
>> + */
>> + rseq_set_notify_resume(current);
>> + }
>> +
>> + return 0;
>> +}
> [...]
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
