vtime: Add HAVE_VIRT_CPU_ACCOUNTING_GEN Kconfig

With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. In order
to use that feature, arch code should be audited to ensure there are no
races in concurrent read/write of cputime_t. For example,
reading/writing 64-bit cputime_t on some 32-bit arches may require
multiple accesses for low and high value parts, so proper locking
is needed to protect against concurrent accesses.

Therefore, add CONFIG_HAVE_VIRT_CPU_ACCOUNTING_GEN which arches can
enable after they've been audited for potential races.

This option is automatically enabled on 64-bit platforms.

Feature requested by Frederic Weisbecker.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arm Linux <linux-arm-kernel@lists.infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

3 files changed, 14 insertions, 0 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index af2cc6eabcc7..185f8b007643 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -353,6 +353,18 @@ config HAVE_CONTEXT_TRACKING
 config HAVE_VIRT_CPU_ACCOUNTING
         bool
 
+config HAVE_VIRT_CPU_ACCOUNTING_GEN
+        bool
+        default y if 64BIT
+        help
+          With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
+          Before enabling this option, arch code must be audited
+          to ensure there are no races in concurrent read/write of
+          cputime_t. For example, reading/writing 64-bit cputime_t on
+          some 32-bit arches may require multiple accesses, so proper
+          locking is needed to protect against concurrent accesses.
+
+
 config HAVE_IRQ_TIME_ACCOUNTING
         bool
         help
diff --git a/init/Kconfig b/init/Kconfig
index 3ecd8a1178f1..68c1a0ed704d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -355,6 +355,7 @@ config VIRT_CPU_ACCOUNTING_NATIVE
 config VIRT_CPU_ACCOUNTING_GEN
         bool "Full dynticks CPU time accounting"
         depends on HAVE_CONTEXT_TRACKING && 64BIT
+        depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
         select VIRT_CPU_ACCOUNTING
         select CONTEXT_TRACKING
         help
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 2b62fe86f9ec..f148475e5194 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -101,6 +101,7 @@ config NO_HZ_FULL
         depends on HAVE_CONTEXT_TRACKING
         # VIRT_CPU_ACCOUNTING_GEN dependency
         depends on 64BIT
+        depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
         select NO_HZ_COMMON
         select RCU_USER_QS
         select RCU_NOCB_CPU