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Commit 663f4c61 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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: default avatarPaolo Bonzini <pbonzini@redhat.com>

Conflicts:
	arch/x86/kvm/x86.c
parent 4a1e10d5

arch/x86/kvm/x86.c

+38 −1
Original line number Diff line number Diff line
@@ -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 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, 


	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;