> -----Original Message----- > From: Wei Liu <wei.liu....@gmail.com> On Behalf Of Wei Liu > Sent: 20 December 2019 21:21 > To: Xen Development List <xen-devel@lists.xenproject.org> > Cc: Durrant, Paul <pdurr...@amazon.com>; Michael Kelley > <mikel...@microsoft.com>; Wei Liu <li...@microsoft.com>; Paul Durrant > <p...@xen.org>; Jan Beulich <jbeul...@suse.com>; Andrew Cooper > <andrew.coop...@citrix.com>; Wei Liu <w...@xen.org>; Roger Pau Monné > <roger....@citrix.com> > Subject: [PATCH 5/4] x86/viridian: drop a wrong invalid value from > reference TSC implementation > > The only invalid value mentioned in Hyper-V TLFS 5.0c is 0. Michael > Kelley confirmed that 0xFFFFFFFF was never used [0]. > > [0] https://lists.xen.org/archives/html/xen-devel/2019-12/msg01564.html > > Signed-off-by: Wei Liu <li...@microsoft.com> > --- > xen/arch/x86/hvm/viridian/time.c | 13 ++++--------- > 1 file changed, 4 insertions(+), 9 deletions(-) > > diff --git a/xen/arch/x86/hvm/viridian/time.c > b/xen/arch/x86/hvm/viridian/time.c > index 6b2d745f3a..b8280a1a60 100644 > --- a/xen/arch/x86/hvm/viridian/time.c > +++ b/xen/arch/x86/hvm/viridian/time.c > @@ -45,14 +45,9 @@ static void update_reference_tsc(const struct domain > *d, bool initialize) > if ( !host_tsc_is_safe() || d->arch.vtsc ) > { > /* > - * The specification states that valid values of TscSequence > range > - * from 0 to 0xFFFFFFFE. The value 0xFFFFFFFF is used to indicate > - * this mechanism is no longer a reliable source of time and that > - * the VM should fall back to a different source. > - * > - * Server 2012 (6.2 kernel) and 2012 R2 (6.3 kernel) actually > - * violate the spec. and rely on a value of 0 to indicate that > this > - * enlightenment should no longer be used. > + * The value 0 is used to indicate this mechanism is no longer a > + * reliable source of time and that the VM should fall back to a > + * different source. > */ > p->tsc_sequence = 0; > > @@ -77,7 +72,7 @@ static void update_reference_tsc(const struct domain *d, > bool initialize) > smp_wmb(); > > seq = p->tsc_sequence + 1; > - if ( seq == 0xFFFFFFFF || seq == 0 ) /* Avoid both 'invalid' values > */ > + if ( seq == 0 ) /* Avoid 'invalid' value */ > seq = 1; > > p->tsc_sequence = seq;
Now that we're just dealing with 0, I think the code would be neater as: seq = p->tsc_sequence + 1; p->tsc_sequence = seq ? seq : 1; /* Avoid 'invalid' value 0 */ Paul > -- > 2.20.1 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
