From: Wei Liu Date: Fri, 20 Dec 2019 21:08:28 +0000 (+0000) Subject: x86/viridian: drop a wrong invalid value from reference TSC implementation X-Git-Tag: 4.14.0-rc1~888 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=c9d9b5f4c9dbc077f2a601f6cd20c075cbbb3cf6;p=xen.git 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 Reviewed-by: Paul Durrant --- diff --git a/xen/arch/x86/hvm/viridian/time.c b/xen/arch/x86/hvm/viridian/time.c index 6b2d745f3a..0f1cd9e208 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; @@ -77,10 +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 */ - seq = 1; - - p->tsc_sequence = seq; + p->tsc_sequence = seq ? seq : 1; /* Avoid 'invalid' value 0 */ } static uint64_t trc_val(const struct domain *d, int64_t offset)