4.17-stable review patch. If anyone has any objections, please let me know.
------------------ From: Hugh Dickins <[email protected]> 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 <[email protected]> Signed-off-by: Hugh Dickins <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Alexander Shishkin <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Stephane Eranian <[email protected]> Cc: [email protected] # v4.14+ Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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; }
