diff options
| -rw-r--r-- | arch/x86/include/asm/kvm_host.h | 1 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 44 |
2 files changed, 30 insertions, 15 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index ddebbe0..8a34fca 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -513,6 +513,7 @@ struct kvm_arch { u64 last_tsc_nsec; u64 last_tsc_offset; u64 last_tsc_write; + u32 last_tsc_khz; struct kvm_xen_hvm_config xen_hvm_config; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 41bb90a..4390f42 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1025,33 +1025,46 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) struct kvm *kvm = vcpu->kvm; u64 offset, ns, elapsed; unsigned long flags; - s64 sdiff; + s64 nsdiff; raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); offset = kvm_x86_ops->compute_tsc_offset(vcpu, data); ns = get_kernel_ns(); elapsed = ns - kvm->arch.last_tsc_nsec; - sdiff = data - kvm->arch.last_tsc_write; - if (sdiff < 0) - sdiff = -sdiff; + + /* n.b - signed multiplication and division required */ + nsdiff = data - kvm->arch.last_tsc_write; +#ifdef CONFIG_X86_64 + nsdiff = (nsdiff * 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)); +#endif + nsdiff -= elapsed; + if (nsdiff < 0) + nsdiff = -nsdiff; /* - * Special case: close write to TSC within 5 seconds of - * another CPU is interpreted as an attempt to synchronize - * The 5 seconds is to accommodate host load / swapping as - * well as any reset of TSC during the boot process. - * - * In that case, for a reliable TSC, we can match TSC offsets, - * or make a best guest using elapsed value. - */ - if (sdiff < nsec_to_cycles(vcpu, 5ULL * NSEC_PER_SEC) && - elapsed < 5ULL * NSEC_PER_SEC) { + * Special case: TSC write with a small delta (1 second) of virtual + * cycle time against real time is interpreted as an attempt to + * synchronize the CPU. + * + * For a reliable TSC, we can match TSC offsets, and for an unstable + * TSC, we add elapsed time in this computation. We could let the + * 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 && + vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) { if (!check_tsc_unstable()) { offset = kvm->arch.last_tsc_offset; pr_debug("kvm: matched tsc offset for %llu\n", data); } else { u64 delta = nsec_to_cycles(vcpu, elapsed); - offset += delta; + data += delta; + offset = kvm_x86_ops->compute_tsc_offset(vcpu, data); pr_debug("kvm: adjusted tsc offset by %llu\n", delta); } ns = kvm->arch.last_tsc_nsec; @@ -1059,6 +1072,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) kvm->arch.last_tsc_nsec = ns; kvm->arch.last_tsc_write = data; kvm->arch.last_tsc_offset = offset; + kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz; kvm_x86_ops->write_tsc_offset(vcpu, offset); raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags); |