From 09a0c3f110b2fbe3bd03817c416d00968666fd74 Mon Sep 17 00:00:00 2001 From: Owen Hofmann Date: Mon, 3 Nov 2014 16:57:18 -0800 Subject: [PATCH] kvm: x86: Fix kvm clock versioning. kvm updates the version number for the guest paravirt clock structure by incrementing the version of its private copy. It does not read the guest version, so will write version = 2 in the first update for every new VM, including after restoring a saved state. If guest state is saved during reading the clock, it could read and accept struct fields and guest TSC from two different updates. This changes the code to increment the guest version and write it back. Signed-off-by: Owen Hofmann Reviewed-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index e0260cc..8bf37d0 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1636,16 +1636,16 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; vcpu->last_guest_tsc = tsc_timestamp; + if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time, + &guest_hv_clock, sizeof(guest_hv_clock)))) + return 0; + /* * The interface expects us to write an even number signaling that the * update is finished. Since the guest won't see the intermediate * state, we just increase by 2 at the end. */ - vcpu->hv_clock.version += 2; - - if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time, - &guest_hv_clock, sizeof(guest_hv_clock)))) - return 0; + vcpu->hv_clock.version = guest_hv_clock.version + 2; /* retain PVCLOCK_GUEST_STOPPED if set in guest copy */ pvclock_flags = (guest_hv_clock.flags & PVCLOCK_GUEST_STOPPED); -- 2.7.4