summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorMarcelo Tosatti <mtosatti@redhat.com>2012-03-08 18:46:57 -0300
committerAvi Kivity <avi@redhat.com>2012-03-20 12:40:36 +0200
commit02626b6af5d2bc62db3bb85fc2891b2725535d44 (patch)
tree8f309c29c021118b72cd7f1323420120a27a676a
parentb74f05d61b73af584d0c39121980171389ecfaaa (diff)
downloadlinux-stable-02626b6af5d2bc62db3bb85fc2891b2725535d44.tar.gz
linux-stable-02626b6af5d2bc62db3bb85fc2891b2725535d44.tar.bz2
linux-stable-02626b6af5d2bc62db3bb85fc2891b2725535d44.zip
KVM: x86: fix kvm_write_tsc() TSC matching thinko
kvm_write_tsc() converts from guest TSC to microseconds, not nanoseconds as intended. The result is that the window for matching is 1000 seconds, not 1 second. Microsecond precision is enough for checking whether the TSC write delta is within the heuristic values, so use it instead of nanoseconds. Noted by Avi Kivity. Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
-rw-r--r--arch/x86/kvm/x86.c19
1 files changed, 10 insertions, 9 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 32096cf6c6c9..7287812eeb72 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1025,7 +1025,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
struct kvm *kvm = vcpu->kvm;
u64 offset, ns, elapsed;
unsigned long flags;
- s64 nsdiff;
+ s64 usdiff;
raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
offset = kvm_x86_ops->compute_tsc_offset(vcpu, data);
@@ -1033,18 +1033,19 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
elapsed = ns - kvm->arch.last_tsc_nsec;
/* n.b - signed multiplication and division required */
- nsdiff = data - kvm->arch.last_tsc_write;
+ usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
- nsdiff = (nsdiff * 1000) / vcpu->arch.virtual_tsc_khz;
+ usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
/* do_div() only does unsigned */
asm("idivl %2; xor %%edx, %%edx"
- : "=A"(nsdiff)
- : "A"(nsdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
+ : "=A"(usdiff)
+ : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
#endif
- nsdiff -= elapsed;
- if (nsdiff < 0)
- nsdiff = -nsdiff;
+ do_div(elapsed, 1000);
+ usdiff -= elapsed;
+ if (usdiff < 0)
+ usdiff = -usdiff;
/*
* Special case: TSC write with a small delta (1 second) of virtual
@@ -1056,7 +1057,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
* compensation code attempt to catch up if we fall behind, but
* it's better to try to match offsets from the beginning.
*/
- if (nsdiff < NSEC_PER_SEC &&
+ if (usdiff < USEC_PER_SEC &&
vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
if (!check_tsc_unstable()) {
offset = kvm->arch.cur_tsc_offset;