On Wed, Jun 08, 2016 at 09:11:39PM +0300, Roman Kagan wrote: > Gradual removal of excessive barriers in pvclock reading functions > (commits 502dfeff239e8313bfbe906ca0a1a6827ac8481b, > a3eb97bd80134ba07864ca00747466c02118aca1) ended up removing too much: > although rdtsc is now orderd WRT other loads, there's no protection > against the compiler reordering the loads of ->version with the loads of > other fields. > > E.g. on my system gcc-5.3.1 generates code which loads ->system_time and > ->flags outside of the ->version test loop. > > (Re)introduce the compiler barriers around accesses to the contents of > pvclock. While at this, make the function a bit more compact by > removing unnecessary local variables. > > Signed-off-by: Roman Kagan <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: [email protected] > Cc: Andy Lutomirski <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: [email protected] > --- > arch/x86/include/asm/pvclock.h | 17 +++++------------ > 1 file changed, 5 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h > index fdcc040..65c4de2 100644 > --- a/arch/x86/include/asm/pvclock.h > +++ b/arch/x86/include/asm/pvclock.h > @@ -80,18 +80,11 @@ static __always_inline > unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src, > cycle_t *cycles, u8 *flags) > { > - unsigned version; > - cycle_t ret, offset; > - u8 ret_flags; > - > - version = src->version; > - > - offset = pvclock_get_nsec_offset(src); > - ret = src->system_time + offset; > - ret_flags = src->flags; > - > - *cycles = ret; > - *flags = ret_flags; > + unsigned version = src->version; > + barrier(); > + *cycles = src->system_time + pvclock_get_nsec_offset(src); > + *flags = src->flags; > + barrier(); > return version;
I have a similar patchset in my mbox starting here: https://lkml.kernel.org/r/[email protected] Care to take a look? Thanks. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
