@@ -1219,6 +1219,10 @@ void do_user_addr_fault(struct pt_regs *regs,
struct mm_struct *mm;
vm_fault_t fault;
unsigned int flags = FAULT_FLAG_DEFAULT;
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ struct vm_area_struct pvma;
+ unsigned long seq;
+#endif
tsk = current;
mm = tsk->mm;
@@ -1316,6 +1320,41 @@ void do_user_addr_fault(struct pt_regs *regs,
}
#endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ count_vm_event(SPF_ATTEMPT);
+ seq = mmap_seq_read_start(mm);
+ if (seq & 1)
+ goto spf_abort;
+ rcu_read_lock();
+ vma = find_vma(mm, address);
+ if (!vma || vma->vm_start > address) {
+ rcu_read_unlock();
+ goto spf_abort;
+ }
+ pvma = *vma;
+ rcu_read_unlock();
+ if (!mmap_seq_read_check(mm, seq))
+ goto spf_abort;
+ vma = &pvma;
+ if (unlikely(access_error(error_code, vma)))
+ goto spf_abort;
+ fault = do_handle_mm_fault(vma, address,
+ flags | FAULT_FLAG_SPECULATIVE, seq, regs);
+
+ /* Quick path to respond to signals */
+ if (fault_signal_pending(fault, regs)) {
+ if (!user_mode(regs))
+ kernelmode_fixup_or_oops(regs, error_code, address,
+ SIGBUS, BUS_ADRERR);
+ return;
+ }
+ if (!(fault & VM_FAULT_RETRY))
+ goto done;
+
+spf_abort:
+ count_vm_event(SPF_ABORT);
+#endif
+
/*
* Kernel-mode access to the user address space should only occur
* on well-defined single instructions listed in the exception
@@ -1412,6 +1451,9 @@ void do_user_addr_fault(struct pt_regs *regs,
}
mmap_read_unlock(mm);
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+done:
+#endif
if (likely(!(fault & VM_FAULT_ERROR)))
return;
@@ -300,6 +300,11 @@ struct vm_userfaultfd_ctx {};
* per VM-area/task. A VM area is any part of the process virtual memory
* space that has a special rule for the page-fault handlers (ie a shared
* library, the executable area etc).
+ *
+ * Note that speculative page faults make an on-stack copy of the VMA,
+ * so the structure size matters.
+ * (TODO - it would be preferable to copy only the required vma attributes
+ * rather than the entire vma).
*/
struct vm_area_struct {
/* The first cache line has the info for VMA tree walking. */
@@ -120,6 +120,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
#ifdef CONFIG_SWAP
SWAP_RA,
SWAP_RA_HIT,
+#endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ SPF_ATTEMPT,
+ SPF_ABORT,
#endif
NR_VM_EVENT_ITEMS
};
@@ -1365,6 +1365,10 @@ const char * const vmstat_text[] = {
"swap_ra",
"swap_ra_hit",
#endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+ "spf_attempt",
+ "spf_abort",
+#endif
#endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
};
#endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */
Attempt speculative mm fault handling first, and fall back to the existing (non-speculative) code if that fails. The speculative handling closely mirrors the non-speculative logic. This includes some x86 specific bits such as the access_error() call. This is why we chose to implement the speculative handling in arch/x86 rather than in common code. The vma is first looked up and copied, under protection of the rcu read lock. The mmap lock sequence count is used to verify the integrity of the copied vma, and passed to do_handle_mm_fault() to allow checking against races with mmap writers when finalizing the fault. Signed-off-by: Michel Lespinasse <michel@lespinasse.org> --- arch/x86/mm/fault.c | 42 +++++++++++++++++++++++++++++++++++ include/linux/mm_types.h | 5 +++++ include/linux/vm_event_item.h | 4 ++++ mm/vmstat.c | 4 ++++ 4 files changed, 55 insertions(+)