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That prepares for a quick check, which avoids the update when > nothing changed. > > Signed-off-by: Thomas Gleixner > > --- > include/linux/rseq.h | 7 +++++-- > include/linux/rseq_types.h | 21 +++++++++++++++++++++ > include/trace/events/rseq.h | 4 ++-- > kernel/rseq.c | 4 ++++ > 4 files changed, 32 insertions(+), 4 deletions(-) > > --- a/include/linux/rseq.h > +++ b/include/linux/rseq.h > @@ -57,6 +57,7 @@ static inline void rseq_virt_userspace_e > static inline void rseq_reset(struct task_struct *t) > { > memset(&t->rseq, 0, sizeof(t->rseq)); > + t->rseq.ids.cpu_cid = ~0ULL; > } > > static inline void rseq_execve(struct task_struct *t) > @@ -70,10 +71,12 @@ static inline void rseq_execve(struct ta > */ > static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) > { > - if (clone_flags & CLONE_VM) > + if (clone_flags & CLONE_VM) { > rseq_reset(t); > - else > + } else { > t->rseq = current->rseq; > + t->rseq.ids.cpu_cid = ~0ULL; > + } > } > > #else /* CONFIG_RSEQ */ > --- a/include/linux/rseq_types.h > +++ b/include/linux/rseq_types.h > @@ -31,17 +31,38 @@ struct rseq_event { > }; > > /** > + * struct rseq_ids - Cache for ids, which need to be updated need -> needs > + * @cpu_cid: Compound of @cpu_id and @mm_cid to make the > + * compiler emit a single compare on 64-bit > + * @cpu_id: The CPU ID which was written last to user space > + * @mm_cid: The MM CID which was written last to user space > + * > + * @cpu_id and @mm_cid are updated when the data is written to user space. > + */ > +struct rseq_ids { > + union { > + u64 cpu_cid; > + struct { > + u32 cpu_id; > + u32 mm_cid; > + }; > + }; > +}; > + > +/** > * struct rseq_data - Storage for all rseq related data > * @usrptr: Pointer to the registered user space RSEQ memory > * @len: Length of the RSEQ region > * @sig: Signature of critial section abort IPs > * @event: Storage for event management > + * @ids: Storage for cached CPU ID and MM CID It's far from clear from the diff, but is there a missing space at the beginning of the line above ? Other than that: Reviewed-by: Mathieu Desnoyers > */ > struct rseq_data { > struct rseq __user *usrptr; > u32 len; > u32 sig; > struct rseq_event event; > + struct rseq_ids ids; > }; > > #else /* CONFIG_RSEQ */ > --- a/include/trace/events/rseq.h > +++ b/include/trace/events/rseq.h > @@ -21,9 +21,9 @@ TRACE_EVENT(rseq_update, > ), > > TP_fast_assign( > - __entry->cpu_id = raw_smp_processor_id(); > + __entry->cpu_id = t->rseq.ids.cpu_id; > __entry->node_id = cpu_to_node(__entry->cpu_id); > - __entry->mm_cid = task_mm_cid(t); > + __entry->mm_cid = t->rseq.ids.mm_cid; > ), > > TP_printk("cpu_id=%d node_id=%d mm_cid=%d", __entry->cpu_id, > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -184,6 +184,10 @@ static int rseq_update_cpu_node_id(struc > rseq_unsafe_put_user(t, node_id, node_id, efault_end); > rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end); > > + /* Cache the user space values */ > + t->rseq.ids.cpu_id = cpu_id; > + t->rseq.ids.mm_cid = mm_cid; > + > /* > * Additional feature fields added after ORIG_RSEQ_SIZE > * need to be conditionally updated only if > -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com