[Xen-changelog] [xen stable-4.2] x86: use native RDTSC(P) execution when guest and host frequencies are the same

[patchbot@xxxxxxx]

commit fffcc45a1d6dd4488f69fa6ba5915857e3f17326
Author:     Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
AuthorDate: Fri May 23 15:33:44 2014 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 23 15:33:44 2014 +0200

    x86: use native RDTSC(P) execution when guest and host frequencies are the 
same
    
    We should be able to continue using native RDTSC(P) execution on
    HVM/PVH guests after migration if host and guest frequencies are
    equal (this includes the case when the frequencies are made equal
    by TSC scaling feature).
    
    This also allows us to revert main part of commit 4aab59a3 (svm: Do not
    intercept RDTSC(P) when TSC scaling is supported by hardware) which
    was wrong: while RDTSC intercepts were disabled domain's vtsc could
    still be set, leading to inconsistent view of guest's TSC.
    
    Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 82713ec8d2b65d17f13e46a131e38bfe5baf8bd6
    master date: 2014-04-22 12:07:37 +0200
---
 xen/arch/x86/hvm/svm/svm.c |    2 +-
 xen/arch/x86/time.c        |   15 +++++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index c4da848..cbdc58a 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -732,7 +732,7 @@ static void svm_set_rdtsc_exiting(struct vcpu *v, bool_t 
enable)
     general1_intercepts &= ~GENERAL1_INTERCEPT_RDTSC;
     general2_intercepts &= ~GENERAL2_INTERCEPT_RDTSCP;
 
-    if ( enable && !cpu_has_tsc_ratio )
+    if ( enable )
     {
         general1_intercepts |= GENERAL1_INTERCEPT_RDTSC;
         general2_intercepts |= GENERAL2_INTERCEPT_RDTSCP;
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 7358551..7b6d557 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -37,6 +37,7 @@
 #include <asm/hpet.h>
 #include <io_ports.h>
 #include <asm/setup.h> /* for early_time_init */
+#include <asm/hvm/svm/svm.h> /* for cpu_has_tsc_ratio */
 #include <public/arch-x86/cpuid.h>
 
 /* opt_clocksource: Force clocksource to one of: pit, hpet, cyclone, acpi. */
@@ -1922,10 +1923,16 @@ void tsc_set_info(struct domain *d,
         d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
         d->arch.tsc_khz = gtsc_khz ? gtsc_khz : cpu_khz;
         set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
-        /* use native TSC if initial host has safe TSC, has not migrated
-         * yet and tsc_khz == cpu_khz */
-        if ( host_tsc_is_safe() && incarnation == 0 &&
-                d->arch.tsc_khz == cpu_khz )
+        /*
+         * Use native TSC if the host has safe TSC and:
+         *  HVM/PVH: host and guest frequencies are the same (either
+         *           "naturally" or via TSC scaling)
+         *  PV: guest has not migrated yet (and thus arch.tsc_khz == cpu_khz)
+         */
+        if ( host_tsc_is_safe() &&
+             ((is_hvm_domain(d) &&
+               (d->arch.tsc_khz == cpu_khz || cpu_has_tsc_ratio)) ||
+              incarnation == 0) )
             d->arch.vtsc = 0;
         else 
             d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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