diff options
| author | Marcelo Tosatti <mtosatti@redhat.com> | 2012-03-08 18:46:57 -0300 |
|---|---|---|
| committer | Avi Kivity <avi@redhat.com> | 2012-03-20 12:40:36 +0200 |
| commit | 02626b6af5d2bc62db3bb85fc2891b2725535d44 (patch) | |
| tree | 8f309c29c021118b72cd7f1323420120a27a676a /arch/x86/kvm/x86.c | |
| parent | b74f05d61b73af584d0c39121980171389ecfaaa (diff) | |
| download | lwn-02626b6af5d2bc62db3bb85fc2891b2725535d44.tar.gz lwn-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>
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 19 |
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; |