From 02626b6af5d2bc62db3bb85fc2891b2725535d44 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Thu, 8 Mar 2012 18:46:57 -0300 Subject: 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 Signed-off-by: Avi Kivity --- arch/x86/kvm/x86.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) (limited to 'arch/x86/kvm/x86.c') 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; -- cgit v1.2.3