• Sam bobroff's avatar
    powerpc/tm: Abort syscalls in active transactions · b4b56f9e
    Sam bobroff authored
    This patch changes the syscall handler to doom (tabort) active
    transactions when a syscall is made and return very early without
    performing the syscall and keeping side effects to a minimum (no CPU
    accounting or system call tracing is performed). Also included is a
    new HWCAP2 bit, PPC_FEATURE2_HTM_NOSC, to indicate this
    behaviour to userspace.
    
    Currently, the system call instruction automatically suspends an
    active transaction which causes side effects to persist when an active
    transaction fails.
    
    This does change the kernel's behaviour, but in a way that was
    documented as unsupported.  It doesn't reduce functionality as
    syscalls will still be performed after tsuspend; it just requires that
    the transaction be explicitly suspended.  It also provides a
    consistent interface and makes the behaviour of user code
    substantially the same across powerpc and platforms that do not
    support suspended transactions (e.g. x86 and s390).
    
    Performance measurements using
    http://ozlabs.org/~anton/junkcode/null_syscall.c indicate the cost of
    a normal (non-aborted) system call increases by about 0.25%.
    Signed-off-by: default avatarSam Bobroff <sam.bobroff@au1.ibm.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    b4b56f9e
cputable.h 1.6 KB