[PATCH 1/2] perf: Fix handling of arch_perf_out_copy_user return value.

From: Jed Davis
Date: Mon Jul 29 2013 - 21:14:51 EST

All architectures except x86 use __copy_from_user_inatomic to provide
arch_perf_out_copy_user; like the other copy_from routines, it returns
the number of bytes not copied. perf was expecting the number of bytes
that had been copied. This change corrects that, and thereby allows
PERF_SAMPLE_STACK_USER to be enabled on non-x86 architectures.

x86 uses copy_from_user_nmi, which deviates from the other copy_from
routines by returning the number of bytes copied. (This cancels out
the effect of perf being backwards; apparently this code has only ever
been tested on x86.) This change therefore adds a second wrapper to
re-reverse it for perf; the next patch in this series will clean it up.

Signed-off-by: Jed Davis <jld@xxxxxxxxxxx>
arch/x86/include/asm/perf_event.h | 9 ++++++++-
kernel/events/internal.h | 11 ++++++++++-
2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 8249df4..ddae5bd 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -274,6 +274,13 @@ static inline void perf_check_microcode(void) { }
static inline void amd_pmu_disable_virt(void) { }

-#define arch_perf_out_copy_user copy_from_user_nmi
+static inline unsigned long copy_from_user_nmi_for_perf(void *to,
+ const void __user *from,
+ unsigned long n)
+ return n - copy_from_user_nmi(to, from, n);
+#define arch_perf_out_copy_user copy_from_user_nmi_for_perf

#endif /* _ASM_X86_PERF_EVENT_H */
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index ca65997..e61b22c 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -81,6 +81,7 @@ static inline unsigned long perf_data_size(struct ring_buffer *rb)
return rb->nr_pages << (PAGE_SHIFT + page_order(rb));

+/* The memcpy_func must return the number of bytes successfully copied. */
#define DEFINE_OUTPUT_COPY(func_name, memcpy_func) \
static inline unsigned int \
func_name(struct perf_output_handle *handle, \
@@ -122,11 +123,19 @@ DEFINE_OUTPUT_COPY(__output_copy, memcpy_common)


+/* arch_perf_out_copy_user must return the number of bytes not copied. */
#ifndef arch_perf_out_copy_user
#define arch_perf_out_copy_user __copy_from_user_inatomic

-DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
+static inline unsigned long perf_memcpy_from_user(void *to,
+ const void __user *from,
+ unsigned long n)
+ return n - arch_perf_out_copy_user(to, from, n);
+DEFINE_OUTPUT_COPY(__output_copy_user, perf_memcpy_from_user)

/* Callchain handling */
extern struct perf_callchain_entry *

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