From 663f4c61b8036fd3a80debbe00b58d198ae63e76 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 25 Jun 2013 18:32:07 +0200 Subject: [PATCH] KVM: x86: handle singlestep during emulation This lets debugging work better during emulation of invalid guest state. This time the check is done after emulation, but before writeback of the flags; we need to check the flags *before* execution of the instruction, we cannot check singlestep_rip because the CS base may have already been modified. Signed-off-by: Paolo Bonzini Conflicts: arch/x86/kvm/x86.c --- arch/x86/kvm/x86.c | 39 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8931318..05afd1a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4971,6 +4971,41 @@ static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7, return dr6; } +static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, int *r) +{ + struct kvm_run *kvm_run = vcpu->run; + + /* + * Use the "raw" value to see if TF was passed to the processor. + * Note that the new value of the flags has not been saved yet. + * + * This is correct even for TF set by the guest, because "the + * processor will not generate this exception after the instruction + * that sets the TF flag". + */ + unsigned long rflags = kvm_x86_ops->get_rflags(vcpu); + + if (unlikely(rflags & X86_EFLAGS_TF)) { + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { + kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1; + kvm_run->debug.arch.pc = vcpu->arch.singlestep_rip; + kvm_run->debug.arch.exception = DB_VECTOR; + kvm_run->exit_reason = KVM_EXIT_DEBUG; + *r = EMULATE_USER_EXIT; + } else { + vcpu->arch.emulate_ctxt.eflags &= ~X86_EFLAGS_TF; + /* + * "Certain debug exceptions may clear bit 0-3. The + * remaining contents of the DR6 register are never + * cleared by the processor". + */ + vcpu->arch.dr6 &= ~15; + vcpu->arch.dr6 |= DR6_BS; + kvm_queue_exception(vcpu, DB_VECTOR); + } + } +} + static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r) { struct kvm_run *kvm_run = vcpu->run; @@ -5117,10 +5152,12 @@ restart: if (writeback) { toggle_interruptibility(vcpu, ctxt->interruptibility); - kvm_set_rflags(vcpu, ctxt->eflags); kvm_make_request(KVM_REQ_EVENT, vcpu); vcpu->arch.emulate_regs_need_sync_to_vcpu = false; kvm_rip_write(vcpu, ctxt->eip); + if (r == EMULATE_DONE) + kvm_vcpu_check_singlestep(vcpu, &r); + kvm_set_rflags(vcpu, ctxt->eflags); } else vcpu->arch.emulate_regs_need_sync_to_vcpu = true; -- 2.7.4