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KVM: x86: handle singlestep during emulation

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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 <pbonzini@redhat.com>

Conflicts:
	arch/x86/kvm/x86.c
This commit is contained in:
Paolo Bonzini 2013-06-25 18:32:07 +02:00
parent 4a1e10d5b5
commit 663f4c61b8
1 changed files with 38 additions and 1 deletions
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39
arch/x86/kvm/x86.c
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@ -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;