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/ ?
Regards,
Boqun
> + * returning to user-space.
> + */
> + rseq_set_notify_resume(current);
> + }
> +
> + return 0;
> +}
[...]
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