Messages in this thread | | | Date | Sun, 12 Jun 2016 18:02:31 +0800 | From | Minfei Huang <> | Subject | Re: [PATCH] x86:pvclock: add missing barriers |
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On 06/08/16 at 09:45P, Borislav Petkov wrote: > 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 <rkagan@virtuozzo.com> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: "H. Peter Anvin" <hpa@zytor.com> > > Cc: x86@kernel.org > > Cc: Andy Lutomirski <luto@kernel.org> > > Cc: Borislav Petkov <bp@suse.de> > > Cc: Paolo Bonzini <pbonzini@redhat.com> > > Cc: stable@vger.kernel.org > > --- > > 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/1464329832-4638-1-git-send-email-mnghuan@gmail.com > > Care to take a look?
Hi, Boris.
I had a vocation last several days, and sorry for replying it later.
As Roman said in this thread, both his and mine are similar way to fix this inconsistent issue, and I have a wrapper function smp_rmb in my patch which the root function is barriers in x86 as well.
Thanks Minfei
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