From bbc49f1202030d8563140f307af3ab541d649bd3 Mon Sep 17 00:00:00 2001 From: Leo Yan Date: Sun, 29 Aug 2021 18:22:37 +0800 Subject: perf auxtrace: Add compat_auxtrace_mmap__{read_head|write_tail} When perf runs in compat mode (kernel in 64-bit mode and the perf is in 32-bit mode), the 64-bit value atomicity in the user space cannot be assured, E.g. on some architectures, the 64-bit value accessing is split into two instructions, one is for the low 32-bit word accessing and another is for the high 32-bit word. This patch introduces weak functions compat_auxtrace_mmap__read_head() and compat_auxtrace_mmap__write_tail(), as their naming indicates, when perf tool works in compat mode, it uses these two functions to access the AUX head and tail. These two functions can allow the perf tool to work properly in certain conditions, e.g. when perf tool works in snapshot mode with only using AUX head pointer, or perf tool uses the AUX buffer and the incremented tail is not bigger than 4GB. When perf tool cannot handle the case when the AUX tail is bigger than 4GB, the function compat_auxtrace_mmap__write_tail() returns -1 and tells the caller to bail out for the error. These two functions are declared as weak attribute, this allows to implement arch specific functions if any arch can support the 64-bit value atomicity in compat mode. Suggested-by: Adrian Hunter Signed-off-by: Leo Yan Acked-by: Adrian Hunter Cc: Alexander Shishkin Cc: Andi Kleen Cc: James Clark Cc: Jiri Olsa Cc: John Garry Cc: Mark Rutland Cc: Mathieu Poirier Cc: Mike Leach Cc: Namhyung Kim Cc: Peter Zijlstra Cc: "Russell King (oracle)" Cc: Suzuki Poulouse Cc: Will Deacon Cc: coresight@lists.linaro.org Cc: linux-arm-kernel@lists.infradead.org Link: http://lore.kernel.org/lkml/20210829102238.19693-2-leo.yan@linaro.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/auxtrace.h | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) (limited to 'tools/perf/util/auxtrace.h') diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h index d68a5e80b217..5f383908ca6e 100644 --- a/tools/perf/util/auxtrace.h +++ b/tools/perf/util/auxtrace.h @@ -440,23 +440,39 @@ struct auxtrace_cache; #ifdef HAVE_AUXTRACE_SUPPORT -static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm) +u64 compat_auxtrace_mmap__read_head(struct auxtrace_mmap *mm); +int compat_auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail); + +static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm, + int kernel_is_64_bit __maybe_unused) { struct perf_event_mmap_page *pc = mm->userpg; - u64 head = READ_ONCE(pc->aux_head); + u64 head; + +#if BITS_PER_LONG == 32 + if (kernel_is_64_bit) + return compat_auxtrace_mmap__read_head(mm); +#endif + head = READ_ONCE(pc->aux_head); /* Ensure all reads are done after we read the head */ smp_rmb(); return head; } -static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail) +static inline int auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail, + int kernel_is_64_bit __maybe_unused) { struct perf_event_mmap_page *pc = mm->userpg; +#if BITS_PER_LONG == 32 + if (kernel_is_64_bit) + return compat_auxtrace_mmap__write_tail(mm, tail); +#endif /* Ensure all reads are done before we write the tail out */ smp_mb(); WRITE_ONCE(pc->aux_tail, tail); + return 0; } int auxtrace_mmap__mmap(struct auxtrace_mmap *mm, -- cgit v1.2.3