From: Sebastian Ott Date: Thu, 12 Oct 2017 11:57:26 +0000 (+0200) Subject: s390/debug: only write data once X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=0dcd91a9e6cc0a401416bbdd34b0a255cde0aee1;p=linux.git s390/debug: only write data once debug_event_common memsets the active debug entry with zeros to prevent stale data leakage. This is overwritten with the actual debug data in the next step. Only write zeros to that part of the debug entry that's not used by new debug data. Micro benchmarks show a 2-10% reduction of cpu cycles with this approach. Signed-off-by: Sebastian Ott Acked-by: Michael Holzheu Signed-off-by: Martin Schwidefsky --- diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c index df916738fbd86..2df679d754546 100644 --- a/arch/s390/kernel/debug.c +++ b/arch/s390/kernel/debug.c @@ -902,8 +902,9 @@ debug_entry_t *debug_event_common(debug_info_t *id, int level, const void *buf, } do { active = get_active_entry(id); - memset(DEBUG_DATA(active), 0, id->buf_size); memcpy(DEBUG_DATA(active), buf, min(len, id->buf_size)); + if (len < id->buf_size) + memset((DEBUG_DATA(active)) + len, 0, id->buf_size - len); debug_finish_entry(id, active, level, 0); len -= id->buf_size; buf += id->buf_size; @@ -934,8 +935,9 @@ debug_entry_t *debug_exception_common(debug_info_t *id, int level, } do { active = get_active_entry(id); - memset(DEBUG_DATA(active), 0, id->buf_size); memcpy(DEBUG_DATA(active), buf, min(len, id->buf_size)); + if (len < id->buf_size) + memset((DEBUG_DATA(active)) + len, 0, id->buf_size - len); debug_finish_entry(id, active, level, len <= id->buf_size); len -= id->buf_size; buf += id->buf_size;