KVM: x86: TSC catchup mode

Negate the effects of AN TYM spell while kvm thread is preempted by tracking
conversion factor to the highest TSC rate and catching the TSC up when it has
fallen behind the kernel view of time.  Note that once triggered, we don't
turn off catchup mode.

A slightly more clever version of this is possible, which only does catchup
when TSC rate drops, and which specifically targets only CPUs with broken
TSC, but since these all are considered unstable_tsc(), this patch covers
all necessary cases.

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 519d6f78498..9e6fe391094 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -384,6 +384,9 @@ struct kvm_vcpu_arch {
         u64 last_host_tsc;
         u64 last_guest_tsc;
         u64 last_kernel_ns;
+        u64 last_tsc_nsec;
+        u64 last_tsc_write;
+        bool tsc_catchup;
 
         bool nmi_pending;
         bool nmi_injected;
@@ -444,6 +447,9 @@ struct kvm_arch {
         u64 last_tsc_nsec;
         u64 last_tsc_offset;
         u64 last_tsc_write;
+        u32 virtual_tsc_khz;
+        u32 virtual_tsc_mult;
+        s8 virtual_tsc_shift;
 
         struct kvm_xen_hvm_config xen_hvm_config;