Messages in this thread | | | Subject | Re: [PATCH] KVM: x86: fix root cause for missed hardware breakpoints | From | Xiao Guangrong <> | Date | Fri, 26 Feb 2016 20:01:22 +0800 |
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On 02/26/2016 07:46 PM, Paolo Bonzini wrote: > 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. > > The original patch is good enough for stable releases before 4.1, since > it does not have any dependencies such as commit ae561edeb421 ("KVM: > x86: DR0-DR3 are not clear on reset", 2015-04-02). > > Cc: stable@vger.kernel.org # 4.1+ > Fixes: 172b2386ed16a9143d9a456aae5ec87275c61489 > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > arch/x86/kvm/x86.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index f4891f2ece23..eaf6ee8c28b8 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2752,7 +2752,6 @@ 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) > @@ -6619,12 +6618,12 @@ 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; > }
It is good to me now. It also can fix the case that the debug registers are changed by the debug-process(gdb/perf) in the context of the vcpu as i described in another thread.
Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
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