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>

1 files changed, 12 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