[Xen-devel] [PATCH v2 12/23] vixen: paravirtualization TSC frequency calculation

[Anthony Liguori <aliguori@xxxxxxxx>]

From: Anthony Liguori <aliguori@xxxxxxxxxx>

Otherwise when time sharing a physical CPU, the calculation can
be bogus resulting in time drift for the guest due to improper
frequency within pvclock.

Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
---
 xen/arch/x86/guest/vixen.c        | 22 ++++++++++++++++++++++
 xen/arch/x86/time.c               |  9 ++++++++-
 xen/include/asm-x86/guest/vixen.h |  2 ++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/guest/vixen.c b/xen/arch/x86/guest/vixen.c
index 1ad5bd7..a1614e0 100644
--- a/xen/arch/x86/guest/vixen.c
+++ b/xen/arch/x86/guest/vixen.c
@@ -120,3 +120,25 @@ void vixen_get_reserved_mem(unsigned long *start_pfn, 
unsigned long *end_pfn)
     /* This is part of the Xen ABI */
     *end_pfn   = 0x100000;
 }
+
+u64 vixen_get_cpu_freq(void)
+{
+    volatile vcpu_time_info_t *timep = &global_si->native.vcpu_info[0].time;
+    vcpu_time_info_t time;
+    uint32_t version;
+    u64 imm;
+
+    do {
+       version = timep->version;
+       rmb();
+       time = *timep;
+    } while ((version & 1) || version != time.version);
+
+    imm = (1000000000ULL << 32) / time.tsc_to_system_mul;
+
+    if (time.tsc_shift < 0) {
+       return imm << -time.tsc_shift;
+    } else {
+       return imm >> time.tsc_shift;
+    }
+}
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 2a87950..04c0fbb 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -36,6 +36,7 @@
 #include <io_ports.h>
 #include <asm/setup.h> /* for early_time_init */
 #include <public/arch-x86/cpuid.h>
+#include <asm/guest/vixen.h>
 
 /* opt_clocksource: Force clocksource to one of: pit, hpet, acpi. */
 static char __initdata opt_clocksource[10];
@@ -1687,6 +1688,12 @@ void __init early_time_init(void)
 
     preinit_pit();
     tmp = init_platform_timer();
+
+    /* We cannot trust calibrated values when running under
+     * a hypervisor. */
+    if ( is_vixen() )
+        tmp = vixen_get_cpu_freq();
+
     plt_tsc.frequency = tmp;
 
     set_time_scale(&t->tsc_scale, tmp);
@@ -2014,7 +2021,7 @@ void tsc_set_info(struct domain *d,
                   uint32_t tsc_mode, uint64_t elapsed_nsec,
                   uint32_t gtsc_khz, uint32_t incarnation)
 {
-    if ( is_idle_domain(d) || is_hardware_domain(d) )
+    if ( is_idle_domain(d) || is_vixen() || is_hardware_domain(d) )
     {
         d->arch.vtsc = 0;
         return;
diff --git a/xen/include/asm-x86/guest/vixen.h 
b/xen/include/asm-x86/guest/vixen.h
index 0c040ee..e6b64f2 100644
--- a/xen/include/asm-x86/guest/vixen.h
+++ b/xen/include/asm-x86/guest/vixen.h
@@ -78,4 +78,6 @@ void __init init_vixen(void);
 
 void __init early_vixen_init(void);
 
+u64 vixen_get_cpu_freq(void);
+
 #endif
-- 
1.9.1


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel