Xiao Guangrong <[email protected]> wrote: > > > 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: [email protected] # 4.1+ >> Fixes: 172b2386ed16a9143d9a456aae5ec87275c61489 >> Signed-off-by: Paolo Bonzini <[email protected]> >> --- >> 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.
Seems correct. The code may be easier to follow if the following line: vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_WONT_EXIT would have been moved out of svm_sync_dirty_debug_regs and vmx_sync_dirty_debug_regs into the flow of vcpu_enter_guest (above). Nadav
