KVM: x86: fix root cause for missed hardware breakpoints

BugLink: http://bugs.launchpad.net/bugs/1555640
commit 70e4da7a8ff62f2775337b705f45c804bb450454 upstream.

Commit 172b2386ed16 ("KVM: x86: fix missed hardware breakpoints",
2016-02-10) worked around a case where the debug registers are not loaded
correctly on preemption and on the first entry to KVM_RUN.

However, Xiao Guangrong pointed out that the root cause must be that
KVM_DEBUGREG_BP_ENABLED is not being set correctly.  This can indeed
happen due to the lazy debug exit mechanism, which does not call
kvm_update_dr7.  Fix it by replacing the existing loop (more or less
equivalent to kvm_update_dr0123) with calls to all the kvm_update_dr*
functions.

Fixes: 172b2386ed16a9143d9a456aae5ec87275c61489
Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 002424e744828e57cade4bb554b20293db6f3a7f..0cce8318f09f167dbf1ff692e6637f653de4740a 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2736,7 +2736,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
        }
 
        kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
-       vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD;
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
@@ -6545,12 +6544,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
         * KVM_DEBUGREG_WONT_EXIT again.
         */
        if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) {
-               int i;
-
                WARN_ON(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP);
                kvm_x86_ops->sync_dirty_debug_regs(vcpu);
-               for (i = 0; i < KVM_NR_DB_REGS; i++)
-                       vcpu->arch.eff_db[i] = vcpu->arch.db[i];
+               kvm_update_dr0123(vcpu);
+               kvm_update_dr6(vcpu);
+               kvm_update_dr7(vcpu);
+               vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
        }
 
        /*