4.17-stable review patch. If anyone has any objections, please let me know.
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From: Hugh Dickins hughd@google.com
commit 2c991e408df6a407476dbc453d725e1e975479e7 upstream.
Markus reported that BTS is sporadically missing the tail of the trace in the perf_event data buffer: [decode error (1): instruction overflow] shown in GDB; and bisected it to the conversion of debug_store to PTI.
A little "optimization" crept into alloc_bts_buffer(), which mistakenly placed bts_interrupt_threshold away from the 24-byte record boundary. Intel SDM Vol 3B 17.4.9 says "This address must point to an offset from the BTS buffer base that is a multiple of the BTS record size."
Revert "max" from a byte count to a record count, to calculate the bts_interrupt_threshold correctly: which turns out to fix problem seen.
Fixes: c1961a4631da ("x86/events/intel/ds: Map debug buffers in cpu_entry_area") Reported-and-tested-by: Markus T Metzger markus.t.metzger@intel.com Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Peter Zijlstra peterz@infradead.org Cc: Arnaldo Carvalho de Melo acme@kernel.org Cc: Alexander Shishkin alexander.shishkin@intel.com Cc: Andi Kleen andi.kleen@intel.com Cc: Dave Hansen dave.hansen@intel.com Cc: Stephane Eranian eranian@google.com Cc: stable@vger.kernel.org # v4.14+ Link: https://lkml.kernel.org/r/alpine.LSU.2.11.1807141248290.1614@eggly.anvils Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/events/intel/ds.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -408,9 +408,11 @@ static int alloc_bts_buffer(int cpu) ds->bts_buffer_base = (unsigned long) cea; ds_update_cea(cea, buffer, BTS_BUFFER_SIZE, PAGE_KERNEL); ds->bts_index = ds->bts_buffer_base; - max = BTS_RECORD_SIZE * (BTS_BUFFER_SIZE / BTS_RECORD_SIZE); - ds->bts_absolute_maximum = ds->bts_buffer_base + max; - ds->bts_interrupt_threshold = ds->bts_absolute_maximum - (max / 16); + max = BTS_BUFFER_SIZE / BTS_RECORD_SIZE; + ds->bts_absolute_maximum = ds->bts_buffer_base + + max * BTS_RECORD_SIZE; + ds->bts_interrupt_threshold = ds->bts_absolute_maximum - + (max / 16) * BTS_RECORD_SIZE; return 0; }