perf/x86: Further optimize copy_from_user_nmi()
Now that we can deal with nested NMI due to IRET re-enabling NMIs and
can deal with faults from NMI by making sure we preserve CR2 over NMIs
we can in fact simply access user-space memory from NMI context.
So rewrite copy_from_user_nmi() to use __copy_from_user_inatomic() and
rework the fault path to do the minimal required work before taking
the in_atomic() fault handler.
In particular avoid perf_sw_event() which would make perf recurse on
itself (it should be harmless as our recursion protections should be
able to deal with this -- but why tempt fate).
Also rename notify_page_fault() to kprobes_fault() as that is a much
better name; there is no notifier in it and its specific to kprobes.
Don measured that his worst case NMI path shrunk from ~300K cycles to
~150K cycles.
Cc: Stephane Eranian <eranian@google.com>
Cc: jmario@redhat.com
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: dave.hansen@linux.intel.com
Tested-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131024105206.GM2490@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 4f74d94..5465b86 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -11,39 +11,26 @@
#include <linux/sched.h>
/*
- * best effort, GUP based copy_from_user() that is NMI-safe
+ * We rely on the nested NMI work to allow atomic faults from the NMI path; the
+ * nested NMI paths are careful to preserve CR2.
*/
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
{
- unsigned long offset, addr = (unsigned long)from;
- unsigned long size, len = 0;
- struct page *page;
- void *map;
- int ret;
+ unsigned long ret;
if (__range_not_ok(from, n, TASK_SIZE))
- return len;
+ return 0;
- do {
- ret = __get_user_pages_fast(addr, 1, 0, &page);
- if (!ret)
- break;
+ /*
+ * Even though this function is typically called from NMI/IRQ context
+ * disable pagefaults so that its behaviour is consistent even when
+ * called form other contexts.
+ */
+ pagefault_disable();
+ ret = __copy_from_user_inatomic(to, from, n);
+ pagefault_enable();
- offset = addr & (PAGE_SIZE - 1);
- size = min(PAGE_SIZE - offset, n - len);
-
- map = kmap_atomic(page);
- memcpy(to, map+offset, size);
- kunmap_atomic(map);
- put_page(page);
-
- len += size;
- to += size;
- addr += size;
-
- } while (len < n);
-
- return len;
+ return n - ret;
}
EXPORT_SYMBOL_GPL(copy_from_user_nmi);
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 3aaeffc..7a517bb 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -51,7 +51,7 @@
return 0;
}
-static inline int __kprobes notify_page_fault(struct pt_regs *regs)
+static inline int __kprobes kprobes_fault(struct pt_regs *regs)
{
int ret = 0;
@@ -1048,7 +1048,7 @@
return;
/* kprobes don't want to hook the spurious faults: */
- if (notify_page_fault(regs))
+ if (kprobes_fault(regs))
return;
/*
* Don't take the mm semaphore here. If we fixup a prefetch
@@ -1060,8 +1060,28 @@
}
/* kprobes don't want to hook the spurious faults: */
- if (unlikely(notify_page_fault(regs)))
+ if (unlikely(kprobes_fault(regs)))
return;
+
+ if (unlikely(error_code & PF_RSVD))
+ pgtable_bad(regs, error_code, address);
+
+ if (static_cpu_has(X86_FEATURE_SMAP)) {
+ if (unlikely(smap_violation(error_code, regs))) {
+ bad_area_nosemaphore(regs, error_code, address);
+ return;
+ }
+ }
+
+ /*
+ * If we're in an interrupt, have no user context or are running
+ * in an atomic region then we must not take the fault:
+ */
+ if (unlikely(in_atomic() || !mm)) {
+ bad_area_nosemaphore(regs, error_code, address);
+ return;
+ }
+
/*
* It's safe to allow irq's after cr2 has been saved and the
* vmalloc fault has been handled.
@@ -1078,27 +1098,8 @@
local_irq_enable();
}
- if (unlikely(error_code & PF_RSVD))
- pgtable_bad(regs, error_code, address);
-
- if (static_cpu_has(X86_FEATURE_SMAP)) {
- if (unlikely(smap_violation(error_code, regs))) {
- bad_area_nosemaphore(regs, error_code, address);
- return;
- }
- }
-
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
- /*
- * If we're in an interrupt, have no user context or are running
- * in an atomic region then we must not take the fault:
- */
- if (unlikely(in_atomic() || !mm)) {
- bad_area_nosemaphore(regs, error_code, address);
- return;
- }
-
if (error_code & PF_WRITE)
flags |= FAULT_FLAG_WRITE;