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authorPeter Zijlstra <peterz@infradead.org>2013-10-24 12:52:06 +0200
committerIngo Molnar <mingo@kernel.org>2013-10-29 12:02:54 +0100
commite00b12e64be9a34ef071de7b6052ca9ea29dd460 (patch)
tree2f3395d06d639550039f3c9aa69c4ad0a4854327 /arch/x86
parent2c42cfbfe10872929c2ba1f8130e31063ff59b94 (diff)
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>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/lib/usercopy.c43
-rw-r--r--arch/x86/mm/fault.c41
2 files changed, 36 insertions, 48 deletions
diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 4f74d94c8d97..5465b8613944 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;
-
- do {
- ret = __get_user_pages_fast(addr, 1, 0, &page);
- if (!ret)
- break;
-
- 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 0;
+
+ /*
+ * 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();
+
+ 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 3aaeffcfd67a..7a517bb41060 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -51,7 +51,7 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr)
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 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
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
@@ -1060,23 +1060,8 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
}
/* kprobes don't want to hook the spurious faults: */
- if (unlikely(notify_page_fault(regs)))
+ if (unlikely(kprobes_fault(regs)))
return;
- /*
- * It's safe to allow irq's after cr2 has been saved and the
- * vmalloc fault has been handled.
- *
- * User-mode registers count as a user access even for any
- * potential system fault or CPU buglet:
- */
- if (user_mode_vm(regs)) {
- local_irq_enable();
- error_code |= PF_USER;
- flags |= FAULT_FLAG_USER;
- } else {
- if (regs->flags & X86_EFLAGS_IF)
- local_irq_enable();
- }
if (unlikely(error_code & PF_RSVD))
pgtable_bad(regs, error_code, address);
@@ -1088,8 +1073,6 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
}
}
- 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:
@@ -1099,6 +1082,24 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
return;
}
+ /*
+ * It's safe to allow irq's after cr2 has been saved and the
+ * vmalloc fault has been handled.
+ *
+ * User-mode registers count as a user access even for any
+ * potential system fault or CPU buglet:
+ */
+ if (user_mode_vm(regs)) {
+ local_irq_enable();
+ error_code |= PF_USER;
+ flags |= FAULT_FLAG_USER;
+ } else {
+ if (regs->flags & X86_EFLAGS_IF)
+ local_irq_enable();
+ }
+
+ perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
+
if (error_code & PF_WRITE)
flags |= FAULT_FLAG_WRITE;