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Subject[BUG] perf: arch_perf_out_copy_user default
Hi Frederic,

I just spotted:

#ifndef arch_perf_out_copy_user
#define arch_perf_out_copy_user __copy_from_user_inatomic
#endif

vs:

arch/x86/include/asm/perf_event.h:#define arch_perf_out_copy_user copy_from_user_nmi


Now the problem is that copy_from_user_nmi() and
__copy_from_user_inatomic() have different return semantics.

Furthermore, the macro you use them in DEFINE_OUTPUT_COPY() assumes the
return value is the amount of memory copied; as also illustrated by
memcpy_common().

Trouble is, __copy_from_user_inatomic() returns the number of bytes
_NOT_ copied.

With this, my question to Will is, how did your ARM unwind support
patches ever work? AFAICT they end up using the
__copy_from_user_inatomic() thing.


---
kernel/events/internal.h | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index ca6599723be5..d7a0f753e695 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -110,7 +110,8 @@ func_name(struct perf_output_handle *handle, \
return len; \
}

-static inline int memcpy_common(void *dst, const void *src, size_t n)
+static inline unsigned long
+memcpy_common(void *dst, const void *src, unsigned long n)
{
memcpy(dst, src, n);
return n;
@@ -123,7 +124,19 @@ DEFINE_OUTPUT_COPY(__output_copy, memcpy_common)
DEFINE_OUTPUT_COPY(__output_skip, MEMCPY_SKIP)

#ifndef arch_perf_out_copy_user
-#define arch_perf_out_copy_user __copy_from_user_inatomic
+#define arch_perf_out_copy_user arch_perf_out_copy_user
+
+static inline unsigned long
+arch_perf_out_copy_user(void *dst, const void *src, unsigned long n)
+{
+ unsigned long ret;
+
+ pagefault_disable();
+ ret = __copy_from_user_inatomic(to, from, n);
+ pagefault_enable();
+
+ return n - ret;
+}
#endif

DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)

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