From: Madhavan Srinivasan maddy@linux.vnet.ibm.com
commit 249fad734a25889a4f23ed014d43634af6798063 upstream.
When a root user or a user with CAP_SYS_ADMIN privilege uses any trace_imc performance monitoring unit events, to monitor application or KVM threads, it may result in a checkstop (System crash).
The cause is frequent switching of the "trace/accumulation" mode of the In-Memory Collection hardware (LDBAR).
This patch disables the trace_imc PMU unit entirely to avoid triggering the checkstop. A future patch will reenable it at a later stage once a workaround has been developed.
Fixes: 012ae244845f ("powerpc/perf: Trace imc PMU functions") Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Madhavan Srinivasan maddy@linux.vnet.ibm.com Tested-by: Hariharan T.S. hari@linux.ibm.com [mpe: Add pr_info_once() so dmesg shows the PMU has been disabled] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20191118034452.9939-1-maddy@linux.vnet.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/platforms/powernv/opal-imc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
--- a/arch/powerpc/platforms/powernv/opal-imc.c +++ b/arch/powerpc/platforms/powernv/opal-imc.c @@ -285,7 +285,14 @@ static int opal_imc_counters_probe(struc domain = IMC_DOMAIN_THREAD; break; case IMC_TYPE_TRACE: - domain = IMC_DOMAIN_TRACE; + /* + * FIXME. Using trace_imc events to monitor application + * or KVM thread performance can cause a checkstop + * (system crash). + * Disable it for now. + */ + pr_info_once("IMC: disabling trace_imc PMU\n"); + domain = -1; break; default: pr_warn("IMC Unknown Device type \n");