From 71341d23668b1700cd50c0abd74073e4351acbd9 Mon Sep 17 00:00:00 2001 From: David Cunado Date: Wed, 19 Jul 2017 12:14:07 +0100 Subject: [PATCH] Address edge case for stale PSCI CPU data in cache There is a theoretical edge case during CPU_ON where the cache may contain stale data for the target CPU data - this can occur under the following conditions: - the target CPU is in another cluster from the current - the target CPU was the last CPU to shutdown on its cluster - the cluster was removed from coherency as part of the CPU shutdown In this case the cache maintenace that was performed as part of the target CPUs shutdown was not seen by the current CPU's cluster. And so the cache may contain stale data for the target CPU. This patch adds a cache maintenance operation (flush) for the cache-line containing the target CPU data - this ensures that the target CPU data is read from main memory. Change-Id: If8cfd42639b03174f60669429b7f7a757027d0fb Signed-off-by: David Cunado --- lib/psci/psci_on.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/lib/psci/psci_on.c b/lib/psci/psci_on.c index 16b22c2ab..d3d0e2ff7 100644 --- a/lib/psci/psci_on.c +++ b/lib/psci/psci_on.c @@ -64,7 +64,20 @@ int psci_cpu_on_start(u_register_t target_cpu, /* * Generic management: Ensure that the cpu is off to be * turned on. + * Perform cache maintanence ahead of reading the target CPU state to + * ensure that the data is not stale. + * There is a theoretical edge case where the cache may contain stale + * data for the target CPU data - this can occur under the following + * conditions: + * - the target CPU is in another cluster from the current + * - the target CPU was the last CPU to shutdown on its cluster + * - the cluster was removed from coherency as part of the CPU shutdown + * + * In this case the cache maintenace that was performed as part of the + * target CPUs shutdown was not seen by the current CPU's cluster. And + * so the cache may contain stale data for the target CPU. */ + flush_cpu_data_by_index(target_idx, psci_svc_cpu_data.aff_info_state); rc = cpu_on_validate_state(psci_get_aff_info_state_by_idx(target_idx)); if (rc != PSCI_E_SUCCESS) goto exit;